Staphylococcus aureus throat colonization is more frequent than colonization in the anterior nares

Abstract

The aim of this study was to determine the frequency and persistence of Staphylococcus aureus carriage in the throat in relation to anterior naris carriage. By use of a sensitive enrichment broth, S. aureus was cultured from the two sites from 259 patients upon admission to an orthopedic ward and from 87 staff members of the same ward. The throat was the most common carriage site in both groups. Forty percent of the patients and 54% of the staff were positive for S. aureus in the throat, compared to 31% and 36%, respectively, in the anterior nares. To determine the persistence of carriage, 67 individuals were repeatedly sampled from the anterior nares and the throat over 2 years (5 to 10 sampling occasions; mean, 7.8). The majority, 58% (39/67), were defined as persistent carriers of S. aureus, considering culture results from both sites. Of the 39 persistent carriers, 15 individuals were culture positive from only the throat on more than half of the sampling occasions (these are called preferential throat carriers) while only 5% (two individuals) were preferential anterior naris carriers by use of the same definition. Typing of the collected S. aureus isolates by pulsed-field gel electrophoresis revealed that the same strain of S. aureus was present, over time, in the throat of an individual at least to the same extent as in the anterior nares. Throat carriage was at least as persistent as carriage in the anterior nares.

FIG. 1.

S. aureus isolation rates among staff and patients at the orthopedic ward from March to September 2003.

FIG. 2.

S. aureus carriage in the anterior nares and the throat among 39 persistent carriers. A red box represents positive results only from the anterior nares on that sampling occasion, an orange box positive from the anterior nares and the throat, a yellow box positive only from the throat, a blue box negative in both locations, and a gray box means no sample was taken. The letter(s) in each box designates the clonal type(s) of the isolated S. aureus strains as determined by PFGE. In orange boxes (positive in anterior nares and throat), the first letter gives the clonal type in the anterior nares and the second in the throat. “$” represents a clonal type unique for that individual. Sampling times are indicated at the top with the following abbreviations: M3, March 2003; A, April 2003; Mj, May to June 2003; Jn, June 2003; J, July 2003; Au, August 2003; S, September 2003; O, October 2003; N, November 2003; D, December 2003; J, January 2004; F, February 2004; M4, March 2004; A5, April 2005.

FIG. 3.

SmaI PFGE band patterns for S. aureus strains isolated from four individuals defined as preferential throat carriers (individuals 5, 9, 12, and 13 [Fig. 2]). Sampling times are indicated above the samples with the following abbreviations: m3, March 2003; A, April 2003; M, May 2003; J, June 2003; Au, August 2003; S, September 2003; N, November 2003; m4, March 2004; a5, April 2005. Individual 5 was positive in the anterior nares and the throat on two occasions. The samples from the anterior nares are underlined.