title: Pandemic (H1N1) 2009 among quarantined close contacts, Beijing, People's Republic of China.
abstract: We estimated the attack rate of pandemic (H1N1) 2009 and assessed risk factors for infection among close contacts quarantined in Beijing, People's Republic of China. The first 613 confirmed cases detected between May 16 and September 15, 2009, were investigated; 7,099 close contacts were located and quarantined. The attack rate of confirmed infection in close contacts was 2.4% overall, ranging from 0.9% among aircraft passengers to >5% among household members. Risk factors for infection among close contacts were younger age, being a household member of an index case-patient, exposure during the index case-patient's symptomatic phase, and longer exposure. Among close contacts with positive test results at the start of quarantine, 17.2% had subclinical infection. Having contact with a household member and younger age were the major risk factors for acquiring pandemic (H1N1) 2009 influenza virus infection. One person in 6 with confirmed pandemic (H1N1) 2009 was asymptomatic.
authors: Beijing Center for Disease Prevention and Control, Beijing, People's Republic of China.
authors: Xinghuo
authors: X
authors: Pang
authors: Peng
authors: P
authors: Yang
authors: Shuang
authors: S
authors: Li
authors: Li
authors: L
authors: Zhang
authors: Lili
authors: L
authors: Tian
authors: Yang
authors: Y
authors: Li
authors: Bo
authors: B
authors: Liu
authors: Yi
authors: Y
authors: Zhang
authors: Baiwei
authors: B
authors: Liu
authors: Ruogang
authors: R
authors: Huang
authors: Xinyu
authors: X
authors: Li
authors: Quanyi
authors: Q
authors: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D002681:China; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D011790:Quarantine; D012307:Risk Factors; D055815:Young Adult