Objective: Most infections occur during childhood, but the health effects of childhood infection are poorly understood. We investigated whether growth decreases in the 2 months after acute seroconversion.

Methods: We performed a nested case-control study among children 6 months to 12 years of age in a community on the outskirts of Lima, Peru. Health interviews were completed daily. Anthropometric measurements were taken monthly. Sera were collected every 4 months and tested for immunoglobulin G. Two-month height and weight gains of seroconverters were compared with gains of sex, age, and size-matched seronegative controls.

Results: In the 2 months after infection, 26 seroconverters gained a median of 24% less weight than 26 matched controls (interquartile range, 63% less to 21% more). In multivariate analysis, infection attenuated weight gain only among children aged 2 years or older. This decrease was not explained by increased diarrhea.

Conclusions: Seroconversion is associated with a slowing of weight gain in children aged 2 years or older. Reasons for this finding merit additional study.