Attack rate and household secondary attack rate of acute conjunctivitis during an outbreak in South India: A community-based survey

INTRODUCTION: Knowledge on epidemiology of the disease in the contemporary world will help to develop appropriate strategies to curtail the transmission during an outbreak. This study was carried out during an outbreak of conjunctivitis in selected areas of Puducherry, South India, to assess the attack rate of conjunctivitis, identify factors associated with developing conjunctivitis and calculate household secondary attack rate (HSAR) of conjunctivitis and its correlates. METHODOLOGY: During December 2014, a community-based survey was conducted in a selected urban and rural area in Puducherry, South India. Simple random sampling was used to select primary sampling units and systematic sampling to select households. All individuals in the selected households were studied. A questionnaire was used to obtain data on sociodemographic characteristics, conjunctivitis during September-November, 2014, and number of household contacts who developed conjunctivitis within 7 days of index case. The attack rate and HSAR of conjunctivitis was expressed as percentage. Multivariate logistic regression was used to find factors independently associated with developing conjunctivitis and also 100% HSAR. RESULTS: Of 3193 study participants from 772 households, 509 (15.9%, 95% confidence interval 14.7-17.2%) had an attack of conjunctivitis during the reference period. Of the 772 households, 218 (28.2%) had at least one case of conjunctivitis. Of 218 households, 33 (15.1%) households had 100% HSAR. Lower age, not being unemployed, low socioeconomic status, and residing in rural area were independently associated with developing conjunctivitis. Index case being male and living in a household with ≥5 members were independently associated with 100% HSAR. CONCLUSION: In the outbreak under study, more than one-fourth of households had at least one case of conjunctivitis and about one in every six individuals had an attack of conjunctivitis.