A Case Control Study of Bacterial Species and Colony Count in Milk of Breastfeeding Women with Chronic Pain

Abstract

An infectious etiology for chronic breast pain in breastfeeding women continues to be debated. Although recent data suggest that Staphylococcus aureus and coagulase-negative Staphylococcus (CNS) may cause chronic breast pain, no studies have used quantitative cultures to address this question. In this study we compared bacterial species and colony counts between breastfeeding women with (cases) and without (controls) chronic pain. We enrolled 114 breastfeeding women in a prospective cohort study. Cases (n=61), breastfeeding women with breast pain for >1 week and no signs of acute infection, were matched with controls (n=53) by weeks postpartum and parity. More cases had a history of mastitis (14% vs. 2%, p=0.036), cracked nipples (64% vs. 17%, p=0.001), and other breastfeeding difficulties. Enterobacter species growth was less likely in cases (0% vs. 7.5%, p=0.029). Cases had a significantly higher growth of S. aureus (19.7% vs. 1.9%, p=0.003). CNS frequency was similar between groups (75% vs. 79%, p=0.626), but median colony count growth was significantly lower in cases (900 colony-forming units/mL vs. 5,000 colony-forming units/ml, p=0.003). Growth of CNS and S. aureus was negatively correlated (r=-0.265, p=0.004). Higher S. aureus growth in cases supports a pathogenic role for S. aureus and reinforces the need for future antibiotic treatment studies in breastfeeding women with chronic pain. In contrast, similar CNS frequency between groups, lower CNS colony counts in cases, and a negative correlation between S. aureus and CNS growth suggest that neither CNS, nor its overgrowth, causes chronic breast pain.