Shams El Arifeen1, Honorati Masanja2, Ahmed Ehsanur Rahman3. 1. Maternal and Child Health Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh. Electronic address: shams@icddrb.org. 2. Ifakara Health Institute, Dar es Salaam, Tanzania. 3. Maternal and Child Health Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.