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HICNet Medical News Digest      Sun, 20 Aug 1995        Volume 08 : 
Issue 26

Today's Topics:

  AIDS Summary
  The Differences in RK Surgery
  The Fundamentals of MRI and CT Scan
  [MMWR Jul14] Outbreak of Acute Gastroenteritis
  [MMWR] State Surveillance ...

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To: hicnews

                       AIDS Daily Summary

The Centers for Disease Control and Prevention (CDC) National AIDS
Clearinghouse makes available the following information as a public
service only. Providing this information does not constitute endorsement
by the CDC, the CDC Clearinghouse, or any other organization. 
Reproduction
of this text is encouraged; however, copies may not be sold, and the CDC
Clearinghouse should be cited as the source of this information.
Copyright 1995, Information, Inc., Bethesda, MD

     In this issue:
     
*********************************************************************
     "Providers Not Diagnosing HIV in Older Women"
     "Cyclosporin A"
     "PCP Therapy: Aerosolized Pentamidine vs. TMP-SMX"
     "Antiviral Conference Reports"
     "Herpesvirus-Like DNA Sequences in Non-Kaposi's Sarcoma
      Skin Lesions of Transplant Patients"
     "Exercise and HIV Infection"
     "HIV Risk-Related Behaviors among Injection Drug Users
      in Rome: Differences between 1990 and 1992"
     "Protection by Attenuated Simian Immunodeficiency Virus
      in Macaques Against Challenge with Virus-Infected Cells"
     "Itraconazole for Mild Histoplasmosis"
     "Search for HIV-1 Group O Infection in Nigeria"
     "Update: Trends in AIDS Among Men Who Have Sex with Men
      --United States, 1989-1994"
     "Transmission of HIV in Dialysis Centre"
     "Chinese Medicine: Where Does It Work Best in HIV/AIDS?"
     "Outcome of Patients with HIV Infection and Decreased
      Consciousness or Recurrent Seizures"
     "Outcome of Patients with HIV Infection and Decreased
      Consciousness or Recurrent Seizures"
     "Sensitization of T Cells to CD95-Mediated Apoptosis by
      HIV-1 Tat and gp120"
     "Mixed-Strain Infection with a Drug-Sensitive and
      Multidrug-Resistant Strain of Mycobacterium tuberculosis"
     
*********************************************************************

     "Providers Not Diagnosing HIV in Older Women"
     AIDS Alert (06/95) Vol. 10, No. 6, P. 77

     The Centers for Disease Control and Prevention (CDC) in Atlanta
reports that 10 percent of all women diagnosed with AIDS by June
1994 were more than 50 years old.  "These are the invisible
victims of the disease," says Patricia Fleming, head of the
reporting and analysis division of the surveillance branch at the
CDC's National Center for Infectious Diseases.  Midlife-and-older
women are not being diagnosed with AIDS until late in the disease
process, sometimes not until death.  According to Fleming, 43
percent of women over 65 with AIDS died within one month of
diagnosis.  A key factor for providers treating older women, she
says, is to recognize that this group is now acquiring the
disease through heterosexual contact, not just through
transfusions.  "Midlife and Older Women and HIV/AIDS" is the
published report of an American Association of Retired
Persons/Center for Women's Policy Studies seminar in 1993.  The
report raises the issues that--with older women and HIV--many
behavioral and psychological risk factors are overlooked,
diagnosis and treatment of HIV is complicated by other aging
factors, and that socioeconomic and cultural factors limit
patient access to care and treatment.


     "Cyclosporin A"
     Nature (05/18/95) Vol. 375, No. 6528, P. 198
     Ho, David D.; Perelson, Alan S.;  Shaw, George M.

     In response to letters to the editor of Nature, Ho et al. write
that the letters' most important point concerns CD4 lymphocyte
redistribution, rather than proliferation.  Although lymphocyte
re-trafficking is a possible explanation, several observations
argue against it, the authors explain.  First, the increases in
CD4 levels were not temporary, but sustained as long as the
antiviral effect was maintained.  Second, studies have shown that
increases in CD4 counts associated with viral suppression were
associated with significant clinical improvement.  Third, recent
unpublished studies by the authors demonstrate that the
surface-marker phenotypes of CD4 lymphocytes post-therapy differ
greatly from those before treatment.  Our preliminary findings
reveal the expression of several activation markers on many of
the CD4 lymphocytes after treatment--a finding which supports
lymphocyte repopulation by cellular proliferation, but argues
against lymphocyte redistribution, Ho et al. conclude.


     "PCP Therapy: Aerosolized Pentamidine vs. TMP-SMX"
     AIDS Clinical Care (06/95) Vol. 7, No. 6, P. 51

     As part of a randomized study of treatments for Pneumocystis
carinii pneumonia (PCP), researchers assigned 367 patients to 21
days of treatment with either aerosolized pentamidine or
trimethoprim-sulfamethoxazole (TMP-SMX).  Each group also
received placebos imitating the opposite treatment.  After 35
days, mortality in the TMP-SMX group was higher, but not enough
to be statistically significant.  However, significantly more
TMP-SMX recipients changed therapy because of toxicity, while
significantly fewer did so because of slow clinical response.
The greatest difference in response was among patients with an
initial alveolar-arterial oxygen gradient greater than 30 mm Hg.
After six months, there were fewer PCP recurrences with TMP-SMX,
but the survival rates for the two drugs were almost identical.
The researchers concluded that TMP-SMX appears to lead to more
rapid improvements in oxygenation, more treatment successes, and
fewer relapses than aerosolized pentamidine, but they are not
sure why it did not also reduce mortality.


     "Antiviral Conference Reports"
     AIDS Treatment News (05/19/95) No. 223, P. 4
     James, John S.

     Following the Eighth International Conference on Antiviral
Research, 256 abstracts of the drugs presented at this conference
were submitted to the March 1995 issue of Antiviral Research,
some of which are mentioned below.  NIM 811, a derivative of
cyclosporin, has no immune suppressive activity, but is still
active against HIV, according to research conducted by Sandoz.
Ingenol, a compound derived from the dried roots of Euphorbia
Kansui Liou, inhibits HIV in extremely low concentrations of .1
nanomolar, which is thousands of times less than the amount of
AZT required.  Although chemically related to carbovir,
Burroughs-Wellcome's 1592U89 is more active against HIV, more
bioavailable, and can penetrate the brain more easily.  PMEA is
chemically related to the anti-CMV drug cidofovir (HPMPC);
however, PMEA is active against HIV as well as CMV and other
herpes viruses.  In addition to treating alcoholism, Antabuse
targets the "zinc fingers" in HIV proteins.  PETT compounds in
the non-nucleoside RT inhibitors (NNRT) series cause HIV
resistance to develop ten times faster than they do with other
non-nucleoside compounds.  In addition, a new series of NNRTs was
found to cause different mutations than known NNRTs and delay the
development of resistant HIV in combination with other drugs.  As
an approved drug for treating CMV, foscarnet also has anti-HIV
activity when combined with AZT and non-nucleoside RT inhibitors.
Furthermore, different ratios AZT and ddI were tested for the
biochemical activation of these drugs in cells.


     "Herpesvirus-Like DNA Sequences in Non-Kaposi's Sarcoma
      Skin Lesions of Transplant Patients"
     Lancet (05/27/95) Vol. 345, No. 8961, P. 1339
     Rady, Peter L..; Yen, Angela;  Rollefson, Janice L. et al.

     To determine whether herpesvirus-like DNA sequences (KSHV)
were associated with proliferative skin lesions not caused by
Kaposi's sarcoma in non-AIDS immunocompromised patients, Rady et
al. tested 33 skin lesions from 4 HIV-negative organ-transplant
patients receiving immunosuppressive therapy.  Using polymerase
chain reaction (PCR), KSHV sequences were identified in more than
80 percent of these lesions.  The two most frequent lesions
tested were actinic keratosis (AK) and squamous cell carcinoma
(SCC). The prevalence of KSHV was 78 percent in AKs and was 93
percent in SCCs.  The researchers concluded that KSHV is related
to lesions other than KS in non-AIDS immunocompromised patients,
and may also be implicated in the pathogenesis of various kinds
of proliferative skin lesions in organ-transplant patients.


     "Exercise and HIV Infection"
     Advocate (05/30/95) No. 682, P. 49
     Cohan, Gary R.

     Increasingly, studies of HIV-infected people indicate that
regular physical exercise offers significant health benefits.
Scientists have found that a lean body mass is strongly
correlated with survival in people with AIDS.  Indeed, the timing
of death in AIDS patients has been found to be directly related
to the amount of lean body weight loss--independent of T-cell
levels or specific opportunistic infections.  To date, most
efforts to halt the wasting process have concentrated on treating
underlying gastrointestinal disorders, stimulating the appetite
with drugs, and providing extra calories.  While these treatments
do increase body weight, the gain is mostly fat and water.
Common sense and current research, however, support the theory
that one must perform some sort of physical activity to convert
these calories and hormones into lean body mass.  Exercise can
also help HIV-infected people maintain or improve their ability
to perform daily activities, increase energy, improve appetite,
and elevate mood.  Most experts agree that people at risk for
HIV-related wasting syndrome should focus on resistance training,
and avoid burning too many calories.


     "HIV Risk-Related Behaviors among Injection Drug Users
      in Rome: Differences between 1990 and 1992"
     American Journal of Public Health (06/95) Vol.85, No.6, P.829
     Davoli, Marina;  Perucci, Carlo A.;  Abeni, Damiano D. et al.

     The primary risk factor for HIV-1 infection and AIDS in Italy is
injection drug use, accounting for about two-thirds of the total
AIDS cases reported by the end of June 1994.  Between 1990 and
1992, Davoli et al. analyzed injection drug users (IDUs) to
better understand the temporal trends in HIV risk-related
behaviors.  An understanding of these trends may help in
verifying the effectiveness of prevention activities, planning
more appropriate education and treatment interventions, and
providing estimates for the future of the epidemic.  From 1990 to
1992, syringe-sharing decreased among self-reported HIV-infected
IDUs, although there was no change in their sexual behavior.  By
the end of the study, fewer HIV-seronegative IDUs reported
sharing needles than in 1990.  There was, however, no change in
the percentage of seronegative users using previously used
syringes, and a reduction in condom use with primary partners was
seen.  The researchers concluded that there is still a great
potential for HIV transmission among IDUs and from IDUs to the
general public.


     "Protection by Attenuated Simian Immunodeficiency Virus
      in Macaques Against Challenge with Virus-Infected Cells"
     Lancet (05/27/95) Vol. 345, No. 8961, P. 1342
     Almond, N.; Kent, K.;  Cranage, M. et al.

   Almond et al. of England's National Institute for Biological
Standards and Control tried to determine if different attenuated,
or weakened, strains of simian immunodeficiency virus (SIV) could
protect against pathogenic isolates, and if such protection would
be effective against cell-associated and cell-free virus
challenge.  In the study, eight cynomolgus macaques were
vaccinated with attenuated cell-free and cell-associated SIV.
These eight were protected, while the eight controls became
infected after the challenge.  According to the researchers, the
results demonstrate that a live-attenuated vaccine can offer
protection from SIV in macaques.  For use in humans, however,
this method will require an extensive study of the safety of
human retroviruses.  Alternatively, the mechanism of this
protection must be understood and reproduced in a less hazardous
fashion.


     "Itraconazole for Mild Histoplasmosis"
     AIDS Clinical Care (06/95) Vol. 7, No. 6, P. 51

   In an uncontrolled study of 59 AIDS patients, researchers found
that oral itraconazole can be an effective alternative to the
toxic and expensive amphotericin B for the treatment of mild
histoplasmosis.  Compared to the historical controls given for
amphotericin B, the rate of clinical response with clearance of
positive cultures was 85 percent for itraconazole.  Although
fungemia cleared quickly with itraconazole, resolution of fever
and clearance of antigen were slower compared to amphotericin B.
The researchers concluded that itraconazole is safe and effective
induction therapy for mild histoplasmosis, but that it may be
better to continue using amphotericin initially, especially in
patients with any of the risk factors associated with
itraconazole failure.


     "Search for HIV-1 Group O Infection in Nigeria"
     Lancet (06/03/95) Vol. 345, No. 8962, P. 1436
     Dada, Abinbola; Olumide, Yetunde M.;  Henrard, Denis R. et al.

     Dada et al. selected 248 serum samples from commercial sex
workers and patients seen at clinics in Lagos to be tested for
HIV-1 group O.  Of the 182 samples that were reactive to an
enzyme-linked immunoassay (EIA), 61 were HIV western-blot
positive, 73 were indeterminate, and 48 tested negative.  The
other 66 tested EIA negative but had varying numbers of bands.
The samples were sent to Chicago's Abbott Laboratories and to the
Centers for Disease Control and Prevention (CDC) for HIV-1 group
O testing.  At Abbott Laboratories, the samples were tested by
the Clonatech HIV (1+2) EIA, which is generally non-reactive with
group O.  A total of 94 had negative Clonatech results.  Forty of
these 94 were further analyzed for type O reactivity using
"consensus" group O specific peptides for the gp41 area of HIV-1,
but none had group O peptide reactivity.  At the CDC, the samples
were screened by Genetic System's HIV 1/2 EIA.  Sixty-two tested
positive for HIV.  These samples also had no group O reactivity
when tested with EIAs based on synthetic peptides derived from
the V3 loop of the envelope proteins representing group O.


     "Update: Trends in AIDS Among Men Who Have Sex with Men
      --United States, 1989-1994"
     MMWR(06/02/95) Vol. 44, No. 21, P. 401

     Almost 35,000 cases of AIDS among men whose only reported
exposure to HIV was sexual contact with other men were reported
to the Centers for Disease Control and Prevention in 1994.
Between 1989 and 1994, rates of AIDS-defining opportunistic
infections (AIDS-OIs) for men who have sex with men (MSM) rose
more than 30 percent from 12.1 to 15.9 cases per 100,000 males
over the age of 13.  Geographically, there were significant
increases in the Midwest and South, while smaller increases were
seen in the West and the Northeast during that five year period.
There were also varying increases by race and ethnicity.
Proportionately, the greatest leaps were seen among black,
Hispanic, American Indian/Alaskan Native, and Asian/Pacific
Islander males with 79 percent, 61 percent, 77 percent, and 55
percent increase, respectively.  Finally, there were substantial
differences in rates according to the size of the metropolitan
statistical area (MSA).  During 1989, for example, the rates were
lowest in rural areas.  These areas, as well as MSAs with
populations between 50,000 and 1 million, had the highest
percentage increase.

_
                                                  



     "Transmission of HIV in Dialysis Centre"
     Lancet (06/03/95) Vol. 345, No. 8962, P. 1417
     Velandia, Martha; Fridkin, Scott K.;  Cardenas, Victor et al.

     Between January 1992 and December 1993, Velandia et al. conducted
a cohort study to determine the risk factors for HIV
seroconversion at a dialysis center in Colombia, South America.
The investigation was prompted by the discovery of 13
HIV-infected patients at the center in August 1993.  Of the 23
patients studied, 12 tested positive for the HIV antibody during
the epidemic period.  The rate of seroconversion was higher among
patients dialysed at the center while a new HIV seropositive
patient received treatment there, or when the center reprocessed
access needles, dialysers, and bloodlines.  Only two of the nine
HIV seroconverters had HIV risk factors--both having had sex with
prostitutes.  The researchers verified that HIV transmission took
place at the dialysis center.  The probable method of
transmission, they said, was improperly reprocessed patient-care
equipment, most likely access needles.  They cautioned that
because this outbreak was discovered accidentally, similar
transmission could be occurring in many other countries where
low-level disinfectants are used to sterilize critical
patient-care equipment.


     "Chinese Medicine: Where Does It Work Best in HIV/AIDS?"
     AIDS Treatment News (06/02/94) No. 224, P. 8

     For three years, Chinese medical treatment in San Francisco has
been funded by the Ryan White CARE Act, and the American College
of Traditional Chinese Medicine there has treated more than 300
symptomatic HIV-positive individuals in long-term care.  The
conditions which appear to be the most responsive to Chinese
medicine are weight loss, diarrhea/loose stools, abdominal pain,
nausea, headaches, enlarged lymph nodes, and neuropathy.  Many
insurers and other third-party payers are now covering
"alternative" methods, such as traditional Chinese medicine.
Alternative care usually costs much less than Western medicine,
and companies can save money by paying for it.


     "Outcome of Patients with HIV Infection and Decreased
     Consciousness or Recurrent Seizures"
     JAMA (06/14/95) Vol. 273, No. 22, P. 1738
     Bedos, Jean-Pierre

     In response to a letter to the editor of the Journal of the
American Medical Association, Jean-Pierre Bedos asserts that
"neurological failure" is the correct term for his study, which
involved HIV-infected patients treated in an intensive care unit
(ICU).  Although the phrase is imprecise and simplistic in a
diagnostic setting, Bedos believes that his inclusion criteria
were logical and well-suited to the patients in whom altered
consciousness and convulsions were the two primary neurological
reasons for hospital admission.  Patients with isolated
neurological disorders--such as aphasia, hemiparesis, and
hemianopsia--who were not part of the group of patients admitted
to the ICU with altered consciousness were not the focus of the
study.  Bedos concludes that, while nonspecific, the term
"neurological failure" can be appropriate inclusion criterion for
prognostic studies of HIV-positive patients admitted to ICUs.


     "Sensitization of T Cells to CD95-Mediated Apoptosis by
      HIV-1 Tat and gp120"
     Nature (06/08/95) Vol. 375, No. 6531, P. 497
     Westendorp, Michael O.; Frank, Rainer; Ochsenbauer, Christina et 
al.

     The reduction of CD4 T cells in AIDS is associated with the rapid
turnover of HIV-1 and apoptosis.  Although the molecular
mechanism of HIV-related apoptosis is unknown, T-cell apoptosis
may be affected by viral proteins--such as HIV-1 Tat and
gp120--and T-cell-receptor (TCR)-induced apoptosis was recently
shown to involve the CD95 (APO-1/Fas) receptor.  Westendorp et
al. demonstrate that HIV-1 Tat strongly sensitizes TCR- and
CD4(gp120)-induced cell death by upregulation of CD95 ligand
expression.  They observed that Tat concentrations that were
effective in cultures of HIV-1-infected cells were also found in
blood samples from HIV-infected patients.  The findings suggest
that HIV-1 Tat and gp120 hasten CD95-mediated, activation-induced
T-cell apoptosis, a mechanism which may contribute to
AIDS-related CD4 T-cell depletion.


     "Mixed-Strain Infection with a Drug-Sensitive and
      Multidrug-Resistant Strain of Mycobacterium tuberculosis"
     Lancet (06/10/95) Vol. 345, No. 8963, P. 1512
     Theisen, A.; Reichel, C.;  Rusch-Gerdes, S. et al.

     In a letter to the editor published in the Lancet, Theisen et al.
present the case of a patient infected with two different strains
of Mycobacterium tuberculosis, one drug-sensitive and one
multidrug-resistant (MDR).  After being diagnosed with M.
tuberculosis, a 24-year-old Nepalese patient was administered
quadruple therapy with isoniazid, rifampicin, ethambutol, and
pyrazinamide.  After 29 days, therapy with pyrazinamide was
stopped because of substantial hepatoxicity.  The sensitive
strain was repeatedly cultured until day 57 of treatment, at
which time the specimens tested negative.  On day 100, a sputum
sample was again positive for tuberculosis (TB), and was now
resistant to rifampicin and isoniazid.  DNA fingerprinting with
the mixed-linker polymerase chain reaction (PCR) technique showed
the isolate to be completely different from the initial
drug-sensitive one.  The patient improved significantly after
being switched to triple therapy with pyrazinamide, ethambutol,
and prothioamide.  The researchers believe that the incidence of
MDR TB was due to coinfection with two wholly different strains.
They recommend repeated resistance testing, particularly in
patients with delayed response to therapy and in those who come
from high prevalence areas for MDR TB.



------------------------------

To: hicnews

                                  [Image]

The Differences in Radial Keratotomy Surgery

Refractive surgery has received tremendous attention by the press, 
produced
wide interest among patients, and has embraced a large percentage of the
ophthalmic community. The main focus (no pun intended) is to correct 
myopia
or nearsightedness, a condition that affects nearly one-fourth of the
world's population.

In refractive surgery we change the optical properties so that patients 
no
longer require spectacles to see at distance. Figure 1 is a schematic of 
a
normal or emmetropic eye (no correction necessary for clear distance
vision). In myopia the aberrant optical system results in the light rays
being focused in front of the retina. Myopia can be corrected by 
flattening
the cornea so that is has less converging power. Radial keratotomy and
excimer laser are the two most popular approaches. In radial keratotomy 
a
series of deep, radial incisions are made in the cornea and result in
peripheral steeping and central flattening. The desired refractive 
change is
typically controlled by adjusting the number or the length of the 
incisions.
The objective is to obtain the desired effect without causing an
overcorrection and thus pushing patients into an over corrected or
farsighted state. Surgical decisions are based on statistical analysis 
of a
large number of previous surgical procedures. RK can now be done in a
relatively precise manner with rather early visual rehabilitation of the
patients.

The excimer is currently an investigational device. The laser is 
currently
under clinical study in the United States (FDA approval anticipated by 
many
within the next 3-12 months), while it is estimated that over 200,000 
cases
have been performed throughout the world. This laser emits energy at 193
nanometers which causes photochemical breakdown of the corneal tissue 
and
thus ablates or vaporizes tissue with minimal surrounding thermal 
damage.
Delivery systems have been designed which permit the laser to shape the
surface of the cornea much like one would lathe a correction on a 
contact
lens. This allows the surgeon to flatten the central cornea and decrease 
the
optical power of the cornea in a relatively precise manner.

At present we have an ongoing clinical study in radial keratotomy and 
are
performing basic research studies with the Summit excimer laser. We
anticipate that we will participate in an FDA sponsored trial of a new
"second generation" excimer laser (the Schwind Keratom distributed by
Coherent, Inc) in the fall of 1995. Our research interests focus on
evaluating the safety and effectiveness of both modalities of surgery.

In our radial keratotomy study, we have three objectives:

1) We are studying the effects of RK on visual performance as measured 
by
contrast sensitivity testing (the ability to distinguish sinusoidal wave
patterns of increasing frequency). This addresses a different aspect of
visual performance than tested with the high contrast Snellen acuity 
("E")
chart as typically used in the doctor's office.

2) We are measuring the surface topography of the cornea to determine
whether problems of under correction can be ascribed to individual 
incisions
so that any additional surgery to "enhance" the effect can focus on the
individual under corrected incisions.

3) Finally, we are taking the topographical analysis data and performing
sophisticated ray tracing analysis. We compute the actual position on 
the
retina of individual light rays that are refracted by the eye. This 
allows
us to predict the visual performance based on the corneal topography and
centration of the procedure on the cornea.

Our overall outcomes with RK have been favorable with 100 percent of
patients 20/40 or better without correction and no major complications. 
We
have shown that centration of the procedure on the entrance pupil is
important for optimizing visual performance in the mid-range frequency 
of
contrast sensitivity testing. This is contrary to what some experienced
surgeons have taught and should provide a scientific basis for 
developing
optimum centering procedures.

We have also been very active in the basic investigation (non-clinical 
use)
of the excimer laser. Although our Summit excimer has recently been 
approved
for therapeutic keratectomy (removal of scars and surface 
irregularities)
and FDA approval for refractive keratectomy has not yet occurred. 
Worldwide
reports of clinical results with the first generation lasers are very
similar to RK. Approximately 92 percent of eyes are 20/40 or better 
without
correction. However, there is room for improvement. Approximately 3 
percent
of patients lose a significant amount of best corrected visual acuity 
and 8
percent remain significantly over or under corrected.

We have been involved with Coherent Lasers in the development of their 
new
second generation laser, the Keratom. This laser can treat myopia as 
well as
astigmatism. A number of advances, such as computer centration of the
procedure, intraoperative eye tracking and enlarged ablation zones, 
should
provide more precise surgery with more consistent results in a greater 
range
of myopes. The early data from foreign countries with the Schwind 
Keratom
Laser shows 98 percent of the patients are 20/40 or better, with less 
than 1
percent loss of two lines or more best corrected visual acuity.

A second major advance that is planned to be incorporated in the 
upcoming
clinical trial of the Coherent Laser is LASIK (laser assisted in situ
keratomieleasus). In this procedure, a thin flap of tissue is sectioned 
from
the surface of the cornea and left attached with a thin adherent rim or
hinge of tissue. The underlying stromal tissue is then treated very
precisely with the laser and the superficial flap is then replaced back 
on
top of the cornea. This results in a very predictable refractive 
correction
with minimal scarring and pain with almost immediate visual 
rehabilitation.
Patients with low to moderately high myopia can be corrected. Our 
personal
experience with this technique is limited to patients we examined in 
Mexico.
These patients did not experience pain and had excellent outcomes. Their
surfaces were healed within 24 hours and it was difficult to even find 
the
incision. The results from elsewhere in the world are outstanding. I 
believe
that this may be the best refractive technique that the future holds and
anxiously await the results of new FDA sponsored clinical trials.

Robert W. Snyder, M.D., Ph.D.
The University of Arizona
Head, Department of Ophthalmology



------------------------------

To: hicnews

                                  [Image]

Understanding the Fundamentals of Magnetic Resonance Imaging and 
Computed
Tomography

There are three principle cross-sectional diagnostic imaging techniques,
ultrasound, magnetic resonance imaging (MR) and computed tomography 
(CT).
Cross-sectional imaging refers to techniques which produce planar images 
as
cross-sections of the patients' anatomy. Conventional radiographic 
images
are projections where many anatomic structures are superimposed (e.g. 
heart,
mediastinum, lung tissue, spine and soft tissues on a chest X-ray). As 
such,
overlapping shadows on radiographs may obscure disease processes.
Cross-sectional images eliminate overlapping shadows to produce images
rivalling anatomic dissections.

Briefly, ultrasound uses high frequency sound wherein the reflected 
sound is
used to create anatomic images. The technique is portable, relatively
inexpensive and sensitive to vascular flow. Ultrasound needs an acoustic
window for transmitting the sound; it cannot effectively transmit 
through
air (e.g. the lung) nor through bone.

MR uses a strong magnetic field (e.g. 10,000 X stronger than the earth's
magnetic field to energize the protons in water). Radiofrequency (RF) 
pulses
are applied to force the hydrogen nuclei into a higher energy state, and
when the protons return to the ground state, signals are emitted from 
the
hydrogen nuclei. These signals are received by a coil, in essence an
antenna, and formatted into an image by a computer. The rate at which
signals grow is related to T1, the longitudinal relaxation time of the
protons, and the rate at which the signals decay is described by T2, the
transverse relaxation time. The other principal variable is proton 
density
the concentration of mobile protons available to create signal. We make 
the
image using different pulse sequences (the timing at which the RF and
electrical gradients are applied) to maximize image contrast for 
selected
applications. On T1 weighted images, structures with the shortest T1 
appear
brightest. Short T1 confers high signal. Fat is usually the brightest
structure on T1 weighted images and tumors usually appear dark. On T2
weighted images, the structures with the longest T2 will appear 
brightest
the longer the T2 the more slowly the signal decays. Pure water has the
longest T2. Tumors tend to have increased water relative to other 
tissues
and therefore generally appear bright on T2 weighted images.

MR is non-invasive and has been shown to be a safe imaging technique. MR
produces images in any scan plane (e.g. sagittal, coronal or axial). For
neurological (CNS) applications MR has mainly replaced CT for oncologic
imaging. For the body outside of the CNS, MR is often ancillary to CT
because MR takes a few minutes to acquire the images. During this time
physiological motion occurs and degrades the images. The CNS moves much 
less
than the abdomen or chest and accordingly the images are generally 
better in
the CNS. At this time MR is still useful in the chest, abdomen and 
pelvis
for selected applications (e.g. in the liver to diagnose hemangioma MR 
is
probably the exam of choice).

MR is currently getting faster and MR angiography more robust. 
Functional MR
imaging has evolved as a tool for mapping the cerebral cortex and 
studying
tissue oxygenation. MR is also being developed as a technique for 
minimally
invasive surgery.

CT is an older and more mature imaging technology than MR. CT uses X-
rays to
create axial images. The X-ray tube rotates around the patient within 
the CT
scanner gantry. In conventional CT the tube rotates around the patient 
once
with the table position fixed. After tube rotation, the table is 
advanced a
fixed distance (e.g. 8 or 10 mm) and the next slice is acquired. The 
slice
thickness is controlled by collimators which define the thickness of the
X-ray beam.

In CT, contrast depends upon the electron density of the subject being
scanned. Air has the lowest density and hence the lowest attenuation and
appears black on CT. Cortical bone is generally the most attenuating
structure and hence appears the densest or whitest on CT. Density on CT 
is
often described by Hounsefield Units (Sir Hounsefield, a British 
scientist
invented CT). Pure water measures 0 Hounsefield Units or HU and air -
1,000
HU. Very dense structures such as cortical bone might approach +1,000 
HU.
Occasionally we use HU values to characterize a tissue, for example a 
benign
renal cyst should be near water density (0 HU) but for practical 
purposes
would probably be no more than 20 HU. Benign granulomas in the lung are
generally diffusely calcified and over 175 HU on CT.

As stated above, on CT, density depends upon electron density of the 
tissue,
and for soft tissues CT density is directly proportional to the specific
gravity of the tissue. This holds for soft tissues where the dominant 
nuclei
are hydrogen, oxygen and nitrogen. In bones however, calcium causes much
greater absorption of X-rays. Calcium and other heavy atomic elements
interact with the X-rays differently than soft tissues. Heavy nuclei 
absorb
the X-rays through a process called the photoelectric effect; this is
proportional to the atomic number of the element cubed.

Because of its high atomic number, iodine is a very effective X-ray
absorber. Iodinated biocompatible compounds are therefore used as X-ray
contrast agents to increase contrast between vascularized and less well
vascularized tissues on CT.

The speed of conventional CT is limited by the time it takes to perform 
each
scan to acquire a slice as well as the time necessary for table
incrementation. A fast conventional CT scanner might take a second to
acquire a scan and two seconds for table incrementation. Therefore, much 
of
the imaging time is spent not scanning but waiting in between scans. It 
is
desirable to scan quickly for several reasons. When X-ray contrast is 
used,
as is most often the case on CT, it rapidly washes out into the other
tissues. When this happens, the image contrast is lost (e.g. ability to
detect tumors is impaired). When time occurs in between scans, we may 
miss
an important lesion, for example in a cancer patient who breathes
differently between two scans, a nodule might be missed. To maximize
contrast and minimize motion it is best to scan as quickly as possible.

Spiral CT uses continuous table feed with continuous X-ray tube rotation 
to
scan much more quickly than conventional CT. Other than these changes 
and
some software and minor hardware modifications, spiral CT functions
similarly to conventional CT.

Because of its speed and ability to capture the X-ray contrast while it 
is
in its arterial phase, spiral CT can be used to perform CT angiography
(CTA). Although the images are acquired axially, they can be reformatted
into any plane. CTA is already making a significant clinical impact. CTA 
can
be performed with intravenous injections of contrast which is less 
invasive
than standard arteriography. Also, CTA can readily be correlated with 
the
anatomic CT images.

The fastest CT technique is cine CT (Imatron). Cine CT uses an electron 
beam
which is swept around a fixed anode target ring positioned around the
patient. There are no moving parts as in the X-ray tube in the 
conventional

_
                                      

or spiral CT scanners. Cine CT can acquire up to 4 slices simultaneously 
in
under 50 msec per image. The technique has robust cardiac and pulmonary
applications.

In conclusion, we are fortunate in modern medicine to have cross-
sectional
imaging techniques such as ultrasound, MR and CT. These techniques allow 
us
to non-invasively see inside the bodies of our patients. Each technique 
has
its own advantages and limitations. We as radiologists must work 
together
with our clinical colleagues to select the best exam and to perform it
appropriately.

Evan Unger, M.D.

Associate Professor of Radiology

Director Cross Sectional Imaging



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To: hicnews

      Outbreak of Acute Gastroenteritis Attributable to Escherichia coli
               Serotype O104:H21 -- Helena, Montana, 1994

     During February-March, 1994, four persons in Helena, Montana
(1995 population: 24,569), developed bloody diarrhea and severe
abdominal cramps. Stool cultures for Salmonella, Shigella,
Campylobacter, and Escherichia coli O157:H7 were negative; however,
sorbitol-negative E. coli colonies were identified in stools from
all four patients. Isolates from three patients were identified at
CDC as a rare serotype--E. coli O104:H21 that produced Shiga-like
toxin II. This report summarizes the epidemiologic and laboratory
investigations of this outbreak by the Lewis and Clark County
Department of Health and Environmental Sciences, the Montana
Department of Health and Environmental Sciences (MDHES), and CDC.
     A confirmed case was defined as acute infection with E. coli
O104:H21 during February 20-May 25, 1994--based on stool culture or
serologic evidence--in a resident of or a visitor to the Helena
area. A suspected case was defined onset of bloody diarrhea or
abdominal cramps during the same period in a resident of or visitor
to the Helena area. MDHES and county health departments contacted
clinicians, laboratories, and the public through news media reports
and requested that suspected cases be reported.
     Eleven confirmed and seven suspected case-patients were
identified (Figure 1). Manifestations included abdominal cramps (18
[100%]), diarrhea (17 [94%]), bloody stools (16 [89%]), vomiting
(10 [56%]), and fever (six of 15 [40%] for whom information was
available). The median age was 36 years (range: 8-63 years), and 12
(67%) were female. Four (22%) persons were hospitalized.
     Potential sources and risk factors for illness were assessed
by a case-control study that included 17 case-patients and three
age-, sex-, and neighborhood-matched controls for each
case-patient. A history of milk consumption during the 7 days
before illness was reported by all 17 case-patients compared with
40 (83%) of 48* controls (matched odds ratio [OR]=undefined). One
brand of milk (Brand A) was significantly associated with illness:
of those persons who drank milk at home, 11 (92%) of 12
case-patients compared with 17 (47%) of 36 controls reported
drinking Brand A (matched OR=16.0; 95% CI=1.3-492.7). Within this
brand, no specific type of milk product was associated with
illness. Factors not associated with illness included consumption
of other brands of milk, other foods or drinks, and dining in
specific restaurants.
     On May 16, the local and state health departments, the Food
and Drug Administration, and CDC inspected the dairy plant where
Brand A milk was produced. Based on review of the plant's records
for internal microbiologic quality-control testing, on 12 days
during February 1-May 13, 1994, the coliform count exceeded the
state regulation limiting maximum coliform levels in milk products
to less than or equal to 10 coliforms per 100 mL on at least one
ready-for-sale milk product. Cultures from selected
post-pasteurization piping and equipment surfaces in contact with
finished milk products yielded fecal coliforms; however, E. coli
O104:H21 was not isolated from any culture samples obtained at the
dairy. Two farms provided raw milk for this dairy; rectal swabs
obtained from a sample of cattle from these farms did not yield E.
coli O104:H21.
Reported by: K Moore, Lewis and Clark County Dept of Health and
Environmental Sciences; T Damrow, PhD, State Epidemiologist,
Montana Dept of Health and Environmental Sciences; DO Abbott, PhD,
Montana State Public Health Laboratory. S Jankowski, Microbiology
Dept, St. Peter's Community Hospital, Helena. Foodborne and
Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases,
National Center for Infectious Diseases, CDC.
Editorial Note: Shiga-like toxin-producing E. coli (SLTEC) are
well-recognized causes of gastrointestinal illness, including both
bloody and nonbloody diarrhea. E. coli O157:H7, the most common
SLTEC, was recognized as a human pathogen in 1982 during the
investigation of two outbreaks of bloody diarrhea associated with
consumption of commercially sold hamburgers (1). In addition to
causing bloody diarrhea, E. coli O157:H7 is the most common cause
of hemolytic uremic syndrome (HUS) in children. Although other
SLTECs also have been identified in sporadic cases of diarrhea and
HUS, the findings in this report document the first reported
outbreak of a non-O157 SLTEC in the United States, and the first
documentation of illness attributable to Shiga-like toxin-producing
E. coli O104:H21.
     The clinical manifestations of infection in this outbreak were
similar to those reported for patients infected with E. coli
O157:H7 (2). Although HUS is a well-recognized complication of E.
coli O157:H7 infection, no patients developed HUS in this outbreak,
possibly reflecting the limited size of the outbreak and the age
distribution of patients.
     Although most outbreaks of E. coli O157:H7 infection have been
associated with consumption of ground beef, raw milk also transmits
this pathogen (3). Healthy cattle may serve as a reservoir for E.
coli O157:H7 and other serotypes of SLTEC (4). The implication of
milk in the outbreak in Montana suggests that cows were the
original source of this specific strain of E. coli O104:H21.
Although the investigation documented post-pasteurization
contamination of milk products with fecal coliforms, E. coli
O104:H21 was not isolated from cultures obtained at the dairy,
possibly because not all post-pasteurization equipment surfaces
were sampled or because of the absence of the pathogen within the
dairy at the time of the inspection.
     Because the techniques used to identify non-O157 SLTEC are not
available in most laboratories (3), infections caused by this
pathogen are most likely to be unrecognized. Most clinical
laboratories that test for E. coli O157:H7 screen stools on a
special medium (sorbitol-MacConkey agar [SMAC]) because E. coli
O157:H7 isolates do not ferment sorbitol after overnight incubation
(5), and most laboratories routinely discard sorbitol-positive
colonies and sorbitol-negative colonies that do not agglutinate in
O157 antiserum. Therefore, isolates of E. coli O104:H21 and other
non-O157 SLTEC are not recognized. The increased availability in
clinical laboratories of techniques such as testing for Shiga-like
toxin or the genes encoding this protein may enhance the detection
of disease attributable to non-O157 SLTEC.
     When evaluating clusters of patients with bloody diarrhea and
other severe diarrheal illness, health-care providers also should
consider the potential roles of E. coli O104:H21 or another
non-O157 SLTEC. When cultures of stool are negative for specific
pathogens, the state health department can be contacted to
determine whether specimens should be examined further for SLTEC.
When advised, health-care providers should freeze fecal specimens
and store isolates from patients with bloody diarrhea; such
specimens may assist in a subsequent investigation.
References
1. Riley LW, Remis RS, Helgerson SD, et al. Hemorrhagic colitis
associated with a rare Escherichia coli serotype. N Engl J Med
1983;308:681-5.
2. Griffin PM, Ostroff SM, Tauxe RV, et al. Illnesses associated
with Escherichia coli O157:H7 infections. Ann Intern Med
1988;109:705-12.
3. Griffin PM. Escherichia coli O157:H7 and other enterohemorrhagic
Escherichia coli. In: Blaser MJ, Smith PD, Ravdin JI, Greenberg HB,
Guerrant RL, eds. Infections of the gastrointestinal tract. New
York: Raven Press, 1995:739-61.
4. Wells JG, Shipman LD, Greene KE, et al. Isolation of Escherichia
coli serotype O157:H7 and other Shiga-like toxin-producing E. coli
from dairy cattle. J Clin Microbiol 1991;29:985-9.
5. March SB, Rutnam S. Sorbitol-MacConkey medium for detection of
Escherichia coliO157:H7 associated with hemorrhagic colitis. J Clin
Microbiol 1986;23:869-72.
* Persons who responded "Don't know" to any question were excluded
from the analysis.


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To: hicnews

      Statewide Surveillance for Antibiotic-Resistant Bacteria
                    -- New Jersey, 1992-1994
     The increasing occurrence of infection with
antibiotic-resistant microorganisms and other emerging infectious
diseases has required the development of flexible and timely
surveillance systems for monitoring these problems (1,2). To
determine the extent of antibiotic resistance in New Jersey, in
1991 the New Jersey State Department of Health (NJSDOH) initiated
a hospital laboratory isolate-based surveillance system for
antimicrobial-resistant bacteria. This report describes the
surveillance system and summarizes findings during 1992-1994 for
vancomycin-resistant enterococci (VRE)--the most rapidly increasing
antibiotic-resistant bacteria reported by New Jersey hospitals.
     The surveillance system includes the 95 acute-care hospitals
licensed by the state of New Jersey. Organisms targeted for
surveillance include gram-positive cocci resistant to vancomycin,
including VRE; methicillin-resistant Staphylococcus aureus (MRSA);
gram-negative rod-shaped bacteria (GNRs) resistant to imipenem;
GNRs resistant to amikacin; and pneumococcal and other
streptococcal isolates resistant to penicillin. Hospitals submit to
NJSDOH monthly a surveillance report form, which includes the
number of in-patient bloodstream isolates of these organisms and
MRSA isolates from any body site. The New Jersey Administrative
Code, which addresses communicable diseases, and state hospital
licensure standards were modified in 1990 to require hospitals to
submit these data to NJSDOH. Hospitals are contacted by the
surveillance system coordinator to ensure monthly reporting; since
the surveillance system was initiated, all hospitals have submitted
monthly reports (3).
     During 1992-1994, a total of 5916 (81%) bloodstream isolates
reported to this system were MRSA. Of the 1398 non-MRSA bloodstream
isolates, 663 (47%) were VRE. During this period, both the number
of hospitals reporting VRE blood isolates and the number of VRE
isolates increased steadily: in 1992, 33 hospitals reported 99
isolates, while in 1994, 54 hospitals reported 278 isolates (Figure
1). Most of the monthly reports (73%) represent only one reported
isolate per hospital. In 1992, hospitals in 13 of the 21 counties
reported VRE isolates, compared with 20 of 21 counties in 1994.
Reported by: SM Paul, MD, L Finelli, DrPH, G Crane, MPH, KC
Spitalny, MD, State Epidemiologist, New Jersey State Dept of
Health. National Center for Infectious Diseases, CDC.
Editorial Note: The recent national emphasis on emerging infectious
diseases has underscored the problem of antibiotic resistance
involving a variety of nosocomial and community-acquired infections
and has focused attention on the importance of microbiology
laboratories as sources of surveillance information for antibiotic
resistance (1,2). For example, in New Jersey, the increase in both
the number of VRE blood isolates and the number of hospitals
reporting VRE blood isolates from 1992 through 1994 suggests the
emergence of the problem of VRE in that state. Careful monitoring
of such trends in antibiotic resistance in enterococci and other
organisms assists clinicians in selecting antibiotics for their
patients and public health agencies in the development and
implementation of prevention efforts.
     In New Jersey, laboratory-based surveillance for VRE and other
antibiotic-resistant isolates has been developed through
collaboration between the NJSDOH, hospitals, and infectious disease
professionals in the state and because of modification of reporting
regulations. The New Jersey system uses data that are routinely
collected and collated by hospital laboratories and requires few
additional resources. Because this surveillance system is
isolate-based, it does not directly measure changes in the rate of
infection in persons, and NJSDOH has used this system primarily for
sentinel purposes to guide further investigation. For example,
early detection and geographic tracking of VRE in New Jersey
through this system have facilitated collaborative efforts
involving public and private sector and academic organizations to
evaluate risk factors for VRE, treatment options, VRE in vitro
susceptibility to antimicrobial agents before clinical trials, and
the effectiveness of infection-control practices (4-7). These
efforts have, in turn, enabled the NJSDOH to collaborate with
professional organizations (the Infectious Diseases Society of New
Jersey and the New Jersey chapters of the Association for
Professionals in Infection Control and Epidemiology) to develop
recommendations to prevent VRE transmission and have provided a
source of bacterial isolates to assist in research efforts to
develop effective antimicrobial agents against VRE.
References
1. Institute of Medicine. Emerging infections: microbial threats to
health in the United States. Washington, DC: National Academy
Press, 1992.
2. CDC. Addressing emerging infectious disease threats to health:
a prevention strategy for the United States. Atlanta, Georgia: US
Department of Health and Human Services, Public Health Service,
1994.
3. Paul SM, Finelli L, Crance GL, Spitalny KC. A statewide
surveillance system for antimicrobial resistant bacteria--New
Jersey. Infect Control Hosp Epidemiol 1995;16 (in press).
4. Paul SM, Silber JL, Crane G, Kupersmit A, Spitalny K.
Vancomycin-resistant enterococcal (VRE) blood isolates in New
Jersey (NJ) hospitals: an 18 month study. In: Proceedings of the
fourth annual meeting of the Society for Hospital Epidemiology of
America. West Deptford, New Jersey: Society for Hospital
Epidemiology of America, 1994.
5. Paul SM, Noveck H, Silber JL, Wartenberg D, Crane G, Spitalny K.
A statewide study of patient risk factors for vancomycin-resistant
enterococcal bacteremia. In: Proceedings of the fourth annual
meeting of the Society for Hospital Epidemiology of America. West
Deptford, New Jersey: Society for Hospital Epidemiology of America,
1994.
6. Silber JL, Patel M, Paul SM, Kostman JR. Statewide surveillance
of isolates of vancomycin-resistant gram-positive cocci: genotyping
of vancomycin resistance and activity of Quinupristin/Dalfopristin
(RP59500) and other antimicrobials. In: Proceedings of the 34th
Annual Interscience Conference on Antimicrobial Agents and
Chemotherapy. Washington, DC: American Society for Microbiology,
1994.
7. Cronan J, Silber J, Schwarz G, Paul SM. Infection control
practices and the prevalence of vancomycin-resistant enterococci
(VRE) in New Jersey hospitals. In: Proceedings of the 34th Annual
Interscience Conference on Antimicrobial Agents and Chemotherapy.
Washington, DC: American Society for Microbiology, 1994.


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End of HICNet Medical News Digest V08 Issue #26
***********************************************


---
Editor, HICNet Medical Newsletter
Internet: david@stat.com                 FAX: +1 (602) 451-6135

                                  
