Updates

By Carol A. Kemper, MD, FACP

Animal Reservoirs for SARS

Source: ProMED-mail post. April 17, 2004.

Last year, china destroyed thousands of civet cats, either hoping to eradicate a primary reservoir for human infection or to impress an anxious public that their government was doing something. However, the SARS Control and Prevention Team in the Guangdong Province recently reported that in addition to civets, several wild animals, including foxes, hedge-shrews, and cats, also carry antibodies for SARS virus. In addition, screening recipients in 16 different cities in this southern province, the team also found that 105 of 994 people (11%) working in animal markets tested positive for SARS antibodies, but only 4 of 123 (3%) civet handlers tested positive. These data suggest that SARS has been present in a number of different animals, as well as humans, in Southern China, probably for some time. Whether there was a recent shift in transmission patterns or violence remains to be determined.

SARS Screening Identifies TB Cases Instead

Source: MMWR Morb Mort Wkly Rep. 2004;53(15):321-322.

Screening for sars in hospital workers in Taipei, Taiwan, last spring ultimately led to the diagnosis of 60 cases of documented or suspected nosocomial tuberculosis. Increased vigilance for SARS in health care workers in April 2003 initially identified a health care worker with fever and respiratory illness with evidence of a pleural effusion. A pleural biopsy grew Mycobacterium tuberculosis (MTb).

Further investigation found 6 coworkers who also had evidence of MTb. Hospital administration then expanded their search for nosocomially acquired cases and over the next 6 months screened 2872 health care workers, identifying 53 additional cases of suspected or documented MTb. Most of the cases were women (85%), with a median age of 30. The majority of the cases (72%) had chest radiographic evidence consistent with a diagnosis of pulmonary MTb, 8% had pleural involvement, 2% had lymphadenitis, and 18% were unclassified. Most of these were suspected of having early pulmonary involvement, as only 5 of 59 with pleural and pulmonary disease reported symptoms. Sputum smears and/or cultures were positive in 19%; thus, the diagnosis was confirmed in only a small number of cases. Seven of 8 culture-confirmed cases had matching genotypes by RFLP technique.

Further investigation tied the cases back to a single patient with a lengthy 3-month hospital course who required admission to the intensive care unit for ventilatory support. This patient was eventually diagnosed with smear-positive pulmonary MTb. Subsequent analysis confirmed that this patient’s genotype matched that of the 7 HCWs above. While most of those affected were nurses, respiratory technicians and radiology technicians were the hardest hit—reinforcing the need for good infection control techniques during respiratory treatment and suctioning, as well as the vigilant use of personal respiratory protection.

Measles Outbreak Among Chinese Adoptees

Source: MMWR Morb Mortal Wkly Rep. 2004;53(15):323-324.

An outbreak of measles has been identified among 12 young adoptees from China who traveled to the United States with their new families on March 26. Nine of the children, 4 of whom were probably acutely infectious during their flight to the United States, developed measles-like rash; 6 cases have been confirmed serologically. The 12 children were traveling with a group of 11 families and spent ~10 days together during the adoption process in China before boarding their flights. They started out on March 26th on 2 separate flights, with several connecting flights to various destinations within the United States on March 27th ( Washington, Alaska, Florida, New York, and Maryland). They were adopted out of 2 orphanages in the Hunan Province, 1 of which had reported a recent outbreak of measles.

The 9 children were aged 12-18 months and should have been previously vaccinated for measles, according to both Chinese and US health recommendations. Although the United States does not require adoptees to have been vaccinated before entry to the United States (they must be vaccinated within 30 days of entry), prospective parents should be aware of the risk of measles in unvaccinated children and review their children’s vaccination records closely. Having said that, some countries (not necessarily China) have been known to forge vaccine records. Given the excellent track record of vaccination in the United States, people from the United States who traveled on those flights are at low risk for measles. Since the incubation period for measles (7-21 days) has just passed, no secondary cases are likely to occur, although the various public health departments remain vigilant.

The United States remains committed to the goal of eliminating endemic measles in the Western Hemisphere, although the biggest threat to this goal remains the risk of imported measles cases from endemic countries. While measles cases in the Western Hemisphere have dropped by > 90% in the past 10 years, a total of 105 cases were reported in 2003 from 6 different countries—Chile (1), Costa Rica (1), Brazil (2), Canada (15), Mexico (44), and the United States (42). Only Mexico and the United States continue to experience outbreaks. Three outbreaks occurring in Mexico in 2003 were traced back to import ed cases, and 2 of 3 outbreaks occurring in the United States in 2003 were the result of imported infections. The origin of the third out break was not determined. Two measles-related deaths occurred in the United States in 2003, for a case-fatality rate of 4.8%. One of these deaths was an immunosuppressed child who developed neurologic complications; the other was an older man in his 70s. These 2 deaths underscore the risk of imported measles in the United States, despite our excellent track record of vaccination.

Recovery of Vaccinia after Smallpox Inoculation

Source: Clin Infect Dis. 2004;38:536-541.

A good question raised during President Bush’s foiled directive to vaccinate health care workers against smallpox was: How occlusive were those occlusive dressings that individuals wore following inoculation? And what were the risks of autoinoculation or transmission to close contacts? These authors from Vanderbilt University evaluated the recovery of vaccinia virus from the lesions and dressings of 148 subjects who received voluntary smallpox vaccination in 2003. The subjects were divided into 3 groups, who were randomized to receive undiluted vaccine, or 1:5 or 1:10 dilutions of vaccine. Subjects were directed to wear 2 occlusive dressings (an initial waterproof gauze-impregnated transparent bandage [OpSite Post-op] and an outer waterproof semipermeable bandage [Tegaderm]). Inoculation site evaluations were performed by trained personnel every 3-5 days. At each visit, specimens were obtained from the inoculation site, outer dressing surface, and from the contralateral hand for vaccinia culture.

The mean interval to lesion healing was 24 days, with a mean of 9.6 dressing changes. During this time, all 148 vaccinees had positive cultures obtained directly from the lesions. However, only 6 of 918 dressings (0.65%) and 2 of 929 (0.22%) hand specimens were positive. The 6 positive dressings included 2 subjects from each of the 3 vaccine groups. The mean time to a positive dressing was 10 days, although 5 of the 6 occurred within 7-10 days of inoculation. The peak viral titer from dressing and hand specimens was ~ 3-4 logs lower than cultures obtained directly from the lesions, suggesting a lower potential for infectivity.

Although largely reassuring, these data do confirm a low level of risk of transmission of vaccinia virus following inoculation, even with dual occlusive dressings and fairly careful monitoring. While no cases of autoinoculation occurred during this study, it required a total of 1421 dressing changes by trained personnel. Such intensive monitoring and handling of dressing changes would not be feasible on a larger scale, from either a manpower or a cost standpoint.

Risk of Hepatitis A in Travelers to Developing Countries

Source: Teitelbaum P. J Travel Med. 2004;11:102-106.

About 4-28% of cases of hepatitis A occur in travelers. This estimated risk has let to recommendations for hepatitis A vaccination (HAV). Teitelbaum assessed the annual incidence of acute HAV infection in Canadian travelers from 1996 to 2001. During that time, Canadians logged ~36 million days/year of travel to developing countries with an average incidence of HAV infection of 6.15 per 100,000 people. Based on these data, ~1 in 3000 travelers are at risk for HAV infection if they spent 1 month traveling in a developing country—considered the usual duration of such travel. Obviously this risk may vary, depending on the types of activity and the country visited. Extrapolating from these figures (based on USD figures for HAV vaccine), about $360,000 of vaccine would be administered to prevent a single HAV infection in travelers to developing countries. I bet the Canadian Health Care System is trying to decide if the expense is worth it.

Dr. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley, Medical Center, Section Editor, Updates, Section Editor, HIV, is Associate Editor for Infectious Disease Alert.