Pneumococcal mastitis is an extremely rare entity and, to the best of our knowledge, there have been only three other case reports in the literature, two of which were puerperal.
S. pneumoniae is a leading cause of respiratory tract infections and meningitis in both children and adults. It is, however, a rare cause of skin and soft-tissue infections and the cases reported are mostly described in patients who have some degree of immunosuppression [
6]. Our patient, whose case we present here, was a healthy 35-year-old immunocompetent woman and there were no signs of any connective tissue diseases or other coincidental health issues.
Although neither of her babies showed any evidence of a respiratory tract infection prior to our patient’s illness, and testing of the babies was not undertaken due to their unavailability, it appears that the most probable way in which the mother became infected with
S. pneumoniae serotype 19A was from one or both of the nasopharyngeal tracts of the babies during breastfeeding. In both of the previous case reports [
4,
5], the breastfed babies had tested positive on nasopharyngeal swabs and showed symptoms of mild respiratory tract infections, which is consistent with our interpretation of the mode of transmission of the
S. pneumoniae in mastitis. Our patient's twin babies were both routinely vaccinated at two and four months of age with Prevnar-7® (Wyeth, Collegeville, PA, USA), which contains capsular antigens of
S. pneumoniae serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. Thus, the serotype 19A
S. pneumoniae isolated in our patient was not part of the seven-valent pneumococcal conjugate vaccine administered to children in the province of Quebec, where our patient resided at the time of her illness. Current Quebec immunization guidelines recommend vaccination of healthy babies with a pneumococcal seven-valent conjugate vaccine (Prevnar-7®) to be given in three doses administered at two, four and 12 months of age [
7]. However, since the introduction of Prevnar-7®, there has been growing concern of the development and spread of the pneumococcal serotypes not covered in the vaccine. A recent review by Reinert
et al. describes global indicators showing that serotype 19A is now the most prevalent as well as the most increasingly resistant
S. pneumoniae serotype in invasive infections [
8]. The most prevalent serotypes involved in invasive disease in Canada at the time of our patient’s presentation were (in descending order): 19A, 7F, 18C, 6A, 22F, 4, 5, 3 and 23B [
9].
Given these findings, the new 13-valent vaccine (Prevnar-13®) that has recently been licensed in Canada, will likely reduce the increasingly prevalent infection rate from the 19A strain of
S. pneumoniae. This new vaccine contains the same antigens as Prevnar-7® with six additional capsular antigens of serotypes 1, 3, 5, 6A, 7F and 19A [
10], which together comprise 13 of the 91
S. pneumoniae serotypes described thus far [
8].