recent data suggests that even in previously affected groups, communicability does not approach the level seen in cruise ships, but could vary with the bug:
These outbreaks are common especially in settings of crowding and poor sanitation (2,3). Transmission of NLVs in these settings is facilitated by high attack rates (82%) (4), a low infectious dose (<100 virions), the absence of long-lasting immunity, the durability of the organism (5), and the potential for multiple modes of transmission (3,6). In 2001, outbreaks were reported from youth camps in Wisconsin and Florida, resulting in closure of the camps (7; CDC, unpublished data, 2001). This report describes an outbreak of NLV-associated gastroenteritis at a large youth encampment in Virginia and the successful use of control measures to limit spread of illness to other campers. Rapid, effective containment is a central goal of public health response when outbreaks of infectious diseases occur.
In July 2001, a large encampment held every 4 years by a national youth organization began in rural Virginia. Approximately 40,000 campers arrived on July 23 from locations throughout the United States and from several other countries. The camp was divided into 20 subcamps comprising approximately 600 groups of 40--90 campers, who were housed in tents. Groups of campers shared water that was dispensed at multiple central locations, outdoor showers, and flush toilets that drained to septic systems. Meals were prepared in small groups of five to 10 campers. On arrival, each group of campers had a requisite health-screening examination before proceeding to a campsite. Medical and public health personnel screened each group by using a standard interview form that asked about the presence of rashes, vomiting, diarrhea, fever, headache, and cough. Groups of campers in which at least one person had a rash or at least two persons shared other symptoms associated with communicable disease were then referred for in-depth screening by the epidemiology support team. Ill campers were asked about the nature and timing of symptoms, travel history, and the source of food and beverages consumed recently. In addition, campers from each of the 20 subcamps within the 7-square-mile encampment who had vomiting, diarrhea, or other symptoms were assessed daily during the encampment to monitor for outbreaks of illness.
On initial screening, two groups of campers had multiple members with vomiting and diarrhea. Initially, these symptoms were found in six (8%) of 80 campers in group A from Illinois and 15 (18%) of 84 in group B from California; both groups arrived on July 23. On the morning of July 24, five (6%) of 80 members of group C from Oklahoma, camped several miles from the other two groups, were found to have similar symptoms. All illnesses were characterized by an acute onset of malaise, nausea, vomiting, and diarrhea. Symptoms typically lasted 24--48 hours. Review of cases by date of onset suggested an infectious illness that had an incubation period of approximately 24 hours but was inconsistent with a single-point source for all of the outbreaks (Figure). Attack rates were eight (10%) of 80 for group A, 26 (31%) of 84 for group B, and 22 (28%) of 80 for group C. Interviews of patients did not reveal any shared exposures or travel history among the three groups. Stool samples were collected from two (25%) of eight ill campers in group A, two (8%) of 26 ill campers in group B, and four (18%) of 22 ill campers in group C. NLVs were detected by the Virginia Division of Consolidated Laboratory Services by using reverse transcriptase-polymerase chain reaction (RT-PCR) in six of the eight stool samples, two from each group. All strains were tested at CDC and were genetically identical within the portion of the genome sequenced.
Outbreaks in the affected groups lasted 4--9 days, compared with durations of 3--4 weeks in two recent camp-associated outbreaks (7; CDC, unpublished data, 2001). Group A was released from isolation on July 25, group B on July 26, and group C on July 29. No new cases were reported from any of the three groups between the time of release from isolation and the end of the encampment. Of 244 campers in the three groups, 56 (23%) became ill. For the subcamps housing the three affected groups, the average rate of campers who had vomiting or diarrhea was 6.0 per 1,000 campers, compared with 3.7 among nonaffected subcamps.
During May 13--19, 2002, a total of 29 British soldiers and staff of a field hospital in Afghanistan became acutely ill after a short incubation period with vomiting, diarrhea, and fever. This report summarizes the investigation of this outbreak and underscores the importance of the diagnostic capacity for NLVs.
The first three patients presented with severe acute illness characterized by headache, neck stiffness, photophobia, obtundation, and gastrointestinal symptoms, which made the initial diagnosis elusive. The third patient's illness was complicated by disseminated intravascular coagulation. Two of these patients required ventilatory support in the field hospital's intensive care unit. All bacteriologic studies performed at the field hospital's laboratory were negative. Because the cause of the illness was unknown, the field hospital was closed to all but patients with gastrointestinal symptoms. Because of the field conditions at the base and the severity of illness in the initial patients, one patient was evacuated to a U.S. military hospital in Germany, and 10 were evacuated to England. Two medical staff who treated the patients on the flight to England and a third contact at the hospital in England subsequently developed gastroenteritis; two of these persons were hospitalized for several days. All patients recovered rapidly and were discharged. The field hospital has since reopened with enhanced infection-control precautions.
In England, fecal specimens were tested for NLVs by electron microscopy (EM), a new antigen-capture enzyme-linked immunosorbent assay (ELISA), and reverse transcription-polymerase chain reaction (RT-PCR). By EM, clumps of small, round-structured viruses were observed and considered to be consistent with NLVs. This finding was confirmed by ELISA and RT-PCR in specimens from five patients. Partial sequence analysis of the polymerase gene identified the virus as belonging to genogroup II (2), the most common NLV genogroup in the United Kingdom and the United States (3).
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