Original Contribution Person-to-Person Transmission of Hepatitis A Virus in an Urban Area of
Intermediate Endemicity: Implications for Vaccination Strategies J. C. Victor 1 , T. Y. Surdina 2 , S. Z. Suleimenova 3 , M. O. Favorov 4 , B. P. Bell 5 , and A. S. Monto 1 1 Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI. 2 Department of Epidemiology, Republican Sanitary Epidemiology Station, Kazakhstan Ministry of Health, Almaty, Kazakhstan. 3 Virology Reference Laboratory, Republican Sanitary Epidemiology Station, Kazakhstan Ministry of Health, Almaty, Kazakhstan. 4 Division of International Health, Coordinating Ofce for Global Health, Centers for Disease Control and Prevention, Atlanta, GA. 5 Division of Viral Hepatitis, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA. Received for publication June 13, 2005; accepted for publication September 8, 2005. Developing countries with an increasing hepatitis A disease burden may target vaccination to specic groups, such as young children, as an initial control strategy. To better understand transmission of hepatitis A virus in
such countries, the authors prospectively studied household and day-care/school contacts of cases in Almaty,
Kazakhstan. Overall, by the time of identication of symptomatic index cases, half of transmission had already
occurred, having been detected retrospectively. The odds of household contacts becoming infected were 35.4
times those for day-care/school contacts (95% condence interval (CI): 17.5, 71.7). Within households, younger
age of either index cases or susceptible contacts elevated the odds of secondary infection among susceptible
contacts: The presence of a case under 6 years of age raised the odds 4.7 times (95% CI: 1.2, 18.7); and compared
with contacts aged 14 years or older, the odds of infection were increased to 7.7 (95% CI: 1.5, 40.3) and 7.0 (95%
CI: 1.4, 34.3) among contacts aged 06 years and 713 years, respectively. Young children are appropriate targets
for sustainable hepatitis A vaccination programs in areas undergoing hepatitis A epidemiologic transition. If vaccine
is determined to be highly effective postexposure and if it is feasible, vaccinating household contacts could be
a useful additional control strategy. communicable disease control; disease transmission; hepatitis A; hepatitis A vaccines; immunization; vaccination Abbreviations: anti-HAV, antibodies to hepatitis A virus; HAV, hepatitis A virus; IgM, immunoglobulin M; SEA, Sanitary
Epidemiology Authority. The vast majority of the worlds population is still at moderate-to-high risk of hepatitis A virus (HAV) infection
(1). As countries around the world develop economically,
the prevalence of HAV infection will probably fall, but par-
adoxically hepatitis A illness will become a greater public
health problem. This is because the likelihood and severity of symptomatic illness with HAV infection are age-related
(24). Under improved sanitation and living conditions,
people escape infection in early childhood and are left sus-
ceptible in adolescence and adulthood, when risk of severe
disease is higher. Because of the close nature of human
contact, especially among young children, households and Reprint requests to Dr. Arnold S. Monto, Department of Epidemiology, School of Public Health, University of Michigan, 109 Observatory
Street, Ann Arbor, MI 48109 (e-mail: asmonto@umich.edu). 204 Am J Epidemiol 2006;163:204210 American Journal of Epidemiology
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