Carriage of community-associated methicillin-resistant Staphylococcus aureus in a cohort of infants in southern Israel: risk factors and molecular features

Abstract

There are few data about the epidemiology of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) among children in Israel. This study was intended to identify risk factors for CA-MRSA colonization in healthy infants, to characterize the molecular features of colonizing organisms, and to determine whether they are responsible for health care-associated (HA) infections. Nasal cultures and demographic details were collected from a cohort of healthy infants at 5 visits between the ages of 2 and 12 months. Clinical characteristics of pediatric MRSA bloodstream infections (2001 to 2006) and wound cultures collected over 6 months were also studied. Clonal structure was evaluated by multilocus sequence typing. Isolates were studied for the staphylococcal cassette chromosome mec (SCCmec) type and for the presence of Panton-Valentine leukocidin (PVL) genes. MRSA was cultured at least once from 45 of 659 infants (346 Jewish and 313 Bedouin infants). Forty of 45 (89%) isolates were from Bedouin infants. Twenty-nine of 45 (64.4%) belonged to a new clonal complex, designated CC913, that carries SCCmec IV but not the PVL genes. CC913 was also isolated from 9/14 blood cultures and 7/8 wounds. All CC913 infections occurred in Bedouin children, and all but two were HA. In conclusion, Bedouin origin was the main risk factor for carriage of CA-MRSA. CC913 was dominant both in healthy carriers and as a cause of pediatric HA-MRSA bloodstream infections.

FIG. 1.

Prevalences of S. aureus carriage among Jewish (n = 301) (a) and Bedouin (n = 252) (b) infants.

FIG. 2.

New acquisition curve (cumulative) of MSSA carriage in Jewish and Bedouin infants. The P value for ethnicity is given.

FIG. 3.

New acquisition curve (cumulative) of MRSA carriage in Jewish and Bedouin infants (RR for Bedouin infants, 6.62 [95% CI, 2.55 to 17.2]; P < 0.001).

FIG. 4.

Cluster analysis of SmaI macrorestriction patterns of MRSA isolates from healthy infant carriers (n = 45). B, Bedouin; J, Jewish.

FIG. 5.

Clonal structure and SCCmec and agr typing of MRSA isolates from 45 carriers (ca) and 22 clinical isolates (cl). Boldface numbers are STs. Boldface capital letters indicate the corresponding PFGE patterns (Fig. 4). Black lines indicate single-locus variations, and gray lines indicate double-locus variations.