Subclinical mastitis may not reduce breastmilk intake during established lactation

Abstract

Objective: This study determined the effect of subclinical mastitis (SCM) on infant breastmilk intake.

Design: Participants (60 Ghanaian lactating mothers and their infants) were from periurban communities in the Manya Krobo district of Ghana in 2006-2007. Bilateral breastmilk samples were obtained once between months 3 and 6 postpartum and tested for SCM using the California mastitis test (CMT) and the sodium/potassium (Na/K) ratio. Infants' 12-hour breastmilk intake was assessed by test weighing. CMT scoring for SCM diagnosis was scaled as >or=1 = positive (n = 37) and <1 = negative (n = 23). SCM diagnosis was confirmed as a Na/K ratio of >1.0 (n = 14).

Results: Breastmilk intake was nonsignificantly lower among infants whose mothers had elevated Na/K ratios of >1.0 (-65.1 g; 95% confidence interval -141.3 g, 11.1 g). Infants whose mothers were positive for SCM with both CMT and Na/K ratio criteria had significantly lower breastmilk intake (-88.9 g; 95% confidence interval -171.1 g, -6.9 g) compared to those whose mothers tested either negative with both tests or positive on only one. Infant weight (p < 0.01) and frequency of feeding (p = 0.01) were independently associated with breastmilk intake. However, the effect of SCM on breastmilk intake disappeared when infant weight and feeding frequency were included in a multiple linear regression model.

Conclusions: The results of this study did not show an effect of SCM on breastmilk intake among 3-6-month-old infants. A larger sample size with a longitudinal design will be needed in future studies.

FIG. 1.

12-hour breastmilk intake of Ghanaian infants by test for maternal SCM. (A) Intake compared between CMT score groups: CMT = 0 (n = 37) or ≥1 (n = 23). The 25^th and 75^th percentiles are demarcated by the box, the median is represented by the dark horizontal line, and the whiskers represent 1.5 multiplied by the interquartile range. There were no significant differences between groups for both tests. (B) Intake compared between Na/K ratio groups: Na/K ratio ≤1.0 (n = 46) or >1 (n = 14). The 25^th and 75^th percentiles are demarcated by the box, the median is represented by the dark horizontal line, and the whiskers represent 1.5 multiplied by the interquartile range. There were no significant differences between groups for both tests.

FIG. 2.

12-hour breastmilk intake of Ghanaian infants by maternal SCM diagnosis as SCM negative (n = 49) or SCM positive (n = 11). SCM positive includes mothers who had both CMT score ≥1 and Na/K ratio >1.0 in at least one breast; SCM negative includes all other mothers. The 25^th and 75^th percentiles are demarcated by the box, the median is represented by the dark horizontal line, and the whiskers represent 1.5 multiplied by the interquartile range.