Who Gets Symptomatic Zika Virus Infection?

Some evidence suggests that a disproportionate proportion of women and those aged 10 to 39 years are infected with Zika virus (ZIKV). Because symptomatic cases of ZIKV infection are more likely to be reported, this difference may be due to a reporting bias. To examine this issue further, researchers at the CDC conducted a household-based cluster investigation between September and October 2016 in five municipalities in Puerto Rico. Visits to households and surrounding homes were made by a team within 30 days of a confirmed diagnosis of ZIKV infection. Of 923 occupied households, 244 were enrolled and 367 participants were investigated. Of these, 114 (31%) had evidence of ZIKV antibody (79 individuals) or ZIKV nucleic acid (27 individuals).

On multivariable analysis, ZIKV infection was more likely if a household member had a recent illness, in clusters that included more vacant houses, if a mosquito bite occurred at least once weekly, and if the bite occurred in the morning. ZIKV was also more common in those who did not keep their doors and windows shut. However, neither female sex nor age of <40 years were associated with increased risk for ZIKV infection. On the other hand, attributable symptomatic infection rates were higher in women than in men (43% vs. 14%), in those <40 years than in those ≥40 years (62% vs. 18%), and in those with asthma than in those without asthma (48% vs. 25%).