Comparison of secondary attack rates in ger and apartment areas, Mongolia, November 2009 / Монголын Анагаах Ухаан

ABSTRACT

Background: Since its first identification of Pandemic H1N1 2009 in Oct 12, 09 in Mongolia, the cases have increased dramatically spreading in much of cities and provinces of Mongolia. We aimed to identify and compare the transmissibility of the infection in different household settings, so to add understanding of special characteristics of this infection.Methods: We selected 20 laboratory confirmed 2009 H1N1 influenza as the index cases from the National Surveillance System. We searched for Influenza like illness (ILI) cases in the households by questioning index-cases and household-contacts. Secondary case was defined as household-contact who developed one of the signs such as fever, dry cough, sore throat, runny nose and diarrhea within one week of symptom onset in index case. We calculated and compared attack rates in ger and apartment areas.Results: Transmissibility of 2009 H1N1 influenza was studied in 20 households. Each half was from ger and apartment residency of Ulaanbaatar city, Mongolia. The study involved 20 indexcases and 72 household-contacts. Secondary transmission occurred in 13 (65%) households with 22 (30.5%) household cases of probable Pandemic H1N1 influenza virus infection. The incidence in ger and apartment areas was 36.1% and 25.0% relatively. Cases in ger residency were 1.2 times more likely than in apartment residency to develop ILI (RR = 1.2, 95%CI 0.86- 1.60).Conclusions: Overall secondary attack rate in this study was 30.5%, which is similar to that of 30% secondary attack rate for laboratory-confirmed 2009 H1N1 influenza in tourist group members in China. Though statistically not significant, the risk estimation of secondary ILI compared in ger and apartment residency indicates ger area residents have 20% higher risk for ILI development after illness in index case.