Outbreak of chickenpox in a refugee camp of northern Thailand

Although varicella occurs universally, its epidemiology is remarkably different in tropical and temperate areas [1]. In temperate countries, more than 90% of people are infected before adolescence [2], whereas in tropical regions varicella tends to occur at a later age causing many adult cases, suggested by the reports, demonstrating a high prevalence of varicella seronegativity among adolescents and adults [1,3-6].Adult varicella patients are known to develop severe disease with a higher rate of complications than children [7], and pregnant women with primary varicella-zoster virus (VZV) infection are at risk of transmitting the infection to their unborn child causing congenital varicella syndrome. Although these factors indicate that the health burden attributable to varicella disease in tropical settings is much heavier than previously assumed [1], data on mortality and hospital admissions from the tropics are sparse [2]. Here, we report the first description of a varicella outbreak in a refugee camp in a tropical region.The international medical humanitarian organization Médecins Sans Frontières (MSF) began providing medical and logistic aid to ethnic Lao Hmong refugees in Phetchabun Province, northern Thailand in July 2005, and opened the sole outpatient clinic in this camp. People were confined to a guarded, barbed-wire enclosed camp controlled by the Thai military, and one household unit consisting of an average of 5 to 6 persons living in a small barracks. Barracks are clustered close together in a small area of 20 hectares. The total registered population in February 2008 was 7,815, including 1,930 children <5 years old. Although the majority recently fled from Laos, an estimated 1,000 Hmong were from a former refugee camp in central Thailand [8]. On the basis of MSF data in 2007, the average monthly crude mortality rate at the camp was 1.89 per 10,000 persons. Although there is no information on the overall prevalence of HIV infection, no cases were detect