By Carol A. Kemper, MD, FACP
Longer Lasting Smallpox Immunity?
Source: ProMED-mail post. August 30, 2002; www.promedmail.org; Frelinger JA, Garba ML. N Engl J Med. 2002:347:689-690.
Scientists at the University of North Carolina have new evidence that smallpox vaccination may provide at least partial protection for up to 35 years or longer. CD8+ T-lymphocyte cell responses to vaccinia virus were evaluated in persons who had received smallpox vaccine from 1 to 35 years ago. Four were laboratory workers who received smallpox vaccine for occupational exposure within the previous 5 years, 5 had received vaccine from 6 to 35 years earlier, and 4 had received vaccine more than 35 years ago. In those who were recently vaccinated, an average of ~6.5% of CD8+ lymphocytes were activated in vitro, as determined by overnight cell culture, compared with about 6% of cells from subjects vaccinated 5 to 35 years earlier and 4% of those from persons vaccinated more than 35 years ago. This is considered a fairly vigorous immune system response, with very little loss of reactivity over a period of more than 35 years.
Public health officials are cautioning that this data not be overly enthusiastically interpreted, pointing to contradictory data derived in the past. Many experts believe that the benefits of vaccine are probably limited to a 10-year period. However, outbreaks of smallpox occurring in the early 1900s suggested that vaccination provided protection from serious illness and death for up to 50 years. The above laboratory data appear to corroborate those historical reports.
Is There a Rabid Bat in Your Belfry?
Source: Messenger SL, et al. Clin Infect Dis. 2002;35:738-747.
For those of you who recently attended the HIVMA meeting in Chicago, on October 25th you had the opportunity to hear Stan Deresinski’s description of being sprayed by fruit bat urine as he entered his flat in Kampala last spring—raising concerns of possible rabies exposure. Cryptogenic exposure to bats is believed to be the leading cause of human rabies—at least in the United States. Various rabies virus variants have been isolated from nearly all of the 41 bat species found in the United States (see the recent "American Bats" USPS stamp series). While the number of cases of human rabies has steadily decreased in the United States over the past 40 years, at least 1 to 2 cases continue to occur annually. Of the 28 indigenous cases diagnosed in the United States since 1980, an animal bite could not be documented in 25 (89%).
Molecular studies suggest that most of these cryptogenic cases are due to virus variants infecting insectivore bats. Two bat species, the silver-haired bat (Lasionycteris noctivagans) and the eastern pipistrelle (Pipistrelle subflavus), appear to be more frequently associated with human rabies infection, although these bats are seldom found in association with humans or human habitats. Interesting, only a minority of cases of human rabies in this survey was from rabies virus commonly associated with house bats.
Another interesting tidbit: Most cases of human rabies in the United States occur in the fall. Assuming an incubation period of 4-8 weeks, this is consistent with the period of greatest risk of exposure to bats occurring during the late summer months. Although rare, clinicians should be prepared to consider rabies as a cause of acute encephalitis, especially in the late summer and fall.
Nosocomial C difficile: Way Common
Source: Wanahita A, et al. Clin Infect Dis. 2002;34:1585-1592.
A significant proportion of hospital patients with leukocytosis, with or without fever, may have unrecognized Clostridium difficile infection. In a prospective observational study of 400 inpatients with leukocytosis > 15,000 cells/mm3, infection was the leading factor contributing to the elevated white blood count in 52% of cases, followed by physiologic stress (38%), medication or drugs (11%), hematologic malignancy (6%), or necrosis or inflammation (6%). Overall, 34 cases (8.5%) with leukocytosis were diagnosed with C difficile infection. One or more infections were documented in 207 (53%) patients, most commonly pneumonia, followed by UTI, soft tissue infection, and C difficile infection.
In those subjects with leukocytosis > 30,000 cells/mm3, pneumonia was still the leading explanation, but C difficile infection was next most frequent, occurring in 25% of patients who did not have hematologic malignancy. Even in those without obvious diarrhea, C difficile should be strongly considered in any hospital patient with leukocytosis.
Dr. Kemper, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, is Associate Editor of Infectious Disease Alert.
Longer Lasting Smallpox Immunity?; Is There a Rabid Bat in Your Belfry?; Nosocomial C difficile: Way Common
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