Contamination of bottles used for feeding reconstituted powdered infant formula and implications for public health

Aims: Microbial contamination of powdered infant formula (PIF) is known to cause gastrointestinal infections in infants. Of concern is intrinsic contamination of the formula with (for example) Salmonella enterica as well as extrinsic contamination from inappropriate handling or ineffective disinfection. The aim of this study was to evaluate organic and microbial contamination of 'in-use' bottles used for feeding infants powdered formula milk in South Wales, UK. Methods: To establish baseline contamination levels of 'in-use' bottles, 75 'uncleaned' and 150 'cleaned and ready to re-use' bottles used for feeding infants PIF were analyzed. The microbiological analysis included aerobic colony counts (ACCs), presence/absence and counts of Enterobacteriaceae and Staphylococcus aureus. The level of residual adenosine tri-phosphate (ATP) was determined as an indicator of organic soiling. All bottles were sampled in four sites; inner screwcap, bottle interior; bottle outer rim and teat interior. Results: Microbial counts up to 10⁵/area were sampled and ATP levels up to 100,051 relative light units (RLUs) were obtained from 'uncleaned' bottles. Findings varied according to bottle site. Enterobacteriaceae and Staphylococcus aureus were isolated from 12-15% of 'unclean' bottles/components (up to 10² cfu/area sampled) and contamination was most frequently detected from the screw cap and teat interiors. Data indicated that after use, prior to cleaning, considerable microbial and organic soil remained in the cumulative bottles. Of the ready-to-use bottles reportedly cleaned and disinfected, some had ACCs up to 5.8×10⁴ cfu/area sampled. Staphylococcus aureus was detected from 4% bottles/components but no Enterobacteriaceae were detected. Conclusions: Cumulatively, findings indicate the presence of organic soiling and the potential for survival of bacteria between infant feeds. There is a need for effective education on effective bottle decontamination procedures. This may be achieved by using an audience-centred approach to re-enforce messages to parents and caregivers to implement good hygiene practices, effectively wash and rinse items before disinfection and follow manufacturers' guidelines for disinfection.