Epidemiologic risk factors for children with acute lower respiratory tract infection in Buenos Aires, Argentina: a matched case-control study. The risk factors that predisposed 516 hospitalized and 154 ambulatory patients to acute lower respiratory tract infection (ALRI) are examined in a matched case-control study. The control group was selected from children attending immunization and well-baby clinics at the same institution that was treating the children with ALRI. Sex, age, nutritional status, socioeconomic level, as well as season and place of residence were used as matching criteria. Because of their distinct profiles, hospitalized and outpatient groups were analyzed separately. However, the four variables with the highest odds ratios (incidence ratios or relative risk) were found to be the same for both groups. These variables were related to the host's condition (bronchial hyperreactivity, presence of persistent symptoms of the upper respiratory tract), family (presence of acute respiratory tract disease in household members), and environment (indoor contaminants). 