Epidemiological investigation of mixed outbreaks of measles/varicella in hilly villages of district Kangra, Himachal Pradesh, India

Background On 26th September 2006, a local health worker informed us about sudden increased number of cases of fever and rash in three villages of district Kangra. We investigated the suspected outbreak to confirm diagnosis and recommendation to prevent and control.
Methods A case of measles was defined as occurrence of fever with rash in a child between six months to 17 years of age, from 26th September to 2nd week of January, 2007. The information on age, sex, symptoms, signs, date of onset, residence, traveling history treatment taken and assessment of cold chain system was collected. The outbreak was described by place, time and person characteristics. We also conducted a retrospective cohort study among children between 10 months and 15 years of age to estimate the vaccine efficacy. We confirmed diagnosis clinically, epidemiologically and serologically.
Results We identified 29/35 measles and 6/35 were confirmed as epidemiologically linked unvaccinated chickenpox case patients. The overall attack rate (AR) was 8.13%; maximally in the age group of 11-17 years ranging in between 17-35%. Sex specific AR was more (17%) in females. There was neither any death nor any serious complications. The proportion of the children vaccinated was 95% for measles but nil for varicella. Of 35 case-patients, 27 (78%) were vaccinated for measles only with no vitamin A supplementation (relative risk: 5.3; 95% confidence interval: 1.90 – 14.77). The measles vaccine efficacy was estimated to be 82%. 3/3 case-patients for measles IgM antibodies and 2/3 nasopharyngeal swabs were tested positive by PCR and D4 measles strain genotyped.
Conclusion Measles/varicella outbreaks were confirmed. We recommended varicella vaccination, second dose opportunity for measles and vitamin A supplementation to all cases in affected areas

Keywords: Double infection, measles, varicella, outbreak, IgM antibodies

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