Breast milk samples were self-collected by CHAMACOS mothers using a breast milk pump, according to the manufacturer’s instructions. Participants were advised to wash hands and the breast area with soap and water prior to collection. Milk was collected into a sterile breast milk collection bottle, and care was taken to ensure the inside of the bottle did not come into contact with skin, clothes, or other external surfaces. Exposure of the sample to air was minimized. Breast milk samples were aliquotted and stored at −20°C until shipment to the University of California, Berkeley School of Public Health Biorepository (Director: Holland), where they were transferred to long-term storage at −80°C.
Saliva samples were collected from children at 5 years of age using Salivette saliva collection swabs (Sarstedt AG & Co, Nümbrecht, Germany). After the child rinsed his or her mouth with water, Salivette cotton plugs were gently tipped into the mouth to prevent contact with the examiner’s or child’s hands. Children were encouraged to hold the cotton plug in their mouths for up to five minutes to promote maximal saliva absorption and to obtain a representative oral sample, at which point they were instructed to spit the plug back into the Salivette tube. Salivette samples were stored at −20°C until transfer to long-term storage at −80°C.
Saliva samples were collected from children at 5 years of age using Salivette saliva collection swabs (Sarstedt AG & Co, Nümbrecht, Germany). After the child rinsed his or her mouth with water, Salivette cotton plugs were gently tipped into the mouth to prevent contact with the examiner’s or child’s hands. Children were encouraged to hold the cotton plug in their mouths for up to five minutes to promote maximal saliva absorption and to obtain a representative oral sample, at which point they were instructed to spit the plug back into the Salivette tube. Salivette samples were stored at −20°C until transfer to long-term storage at −80°C.