Staphylococcal pyrogenic toxins in infant urine samples; a possible marker of transient bacteraemia

Linda M Harrison ^1*, James A Morris ¹, Robert M Lauder ² and David R Telford ¹

¹ University Hospitals of Morecambe Bay NHS Trust, United Kingdom
² Lancaster University, United Kingdom

^* To whom correspondence should be addressed. E-mail: l.harrison{at}lancaster.ac.uk.

Accepted 1 May 2009

Abstract

Aim: To screen infant urine for staphylococcal pyrogenic toxins as a possible marker for a toxigenic, transient bacteraemia.

Methods: Nasopharyngeal swabs, skin swabs, stool and urine samples were collected from 30 infants at 2 weeks, 10 weeks and 7 months of age when the infants were healthy and from infants of 7 months of age when they had a cold. Samples were cultured and S. aureus isolates identified. Isolates were tested for the production of SEB, SEC and TSST-1. Urine samples were analysed for the presence of the same toxins by ELISA.

Results: Nasopharyngeal carriage of S. aureus decreased with age from 50% at 2 weeks of age to 13% in healthy infants at 7 months of age. Carriage was increased in infants over 7 months of age with a cold (36%). Stool carriage remained constant (37-40%) in healthy infants but increased significantly in infants over 7 months of age with a cold (82%). 13.9% of the isolates produced SEB, 16.7% produced SEC and 18% produced TSST-1. Some isolates produced more than one toxin. 43% of infants were colonised at some time with a toxigenic S. aureus strain. S .aureus toxins were detected in 9 of 101 urine samples. The proportion of positive samples was increased with infection and at 10 weeks of age.

Conclusions: Infants are exposed early in life to S. aureus pyrogenic toxins which can be detected in infant urine samples. Age and infection affect the proportion of positive samples. The pattern of results can be explained by episodes of transient bacteraemia.