Maternal-reported morbidity ( fever , diarrhea , and vomiting ) and serious infectious events ( SIEs ) ( gastroenteritis and lower respiratory tract infections ) were investigated for 751 infants for 2 age periods ( 0-2 .9 and 3-6 mo ) by using generalized linear mixed models with breastfeeding as a time-dependent variable and adjustment for study site , maternal education , economic level , and cotrimoxazole prophylaxis .