Factors affecting pharyngeal Haemophilus influenzae type b colonization rates in children

Abstract

Over 1300 children were studied in an analysis of factors that might affect pharyngeal colonization with H. influenzae type b. Semiquantitative methods for the culture of H. influenzae type b, consisting of inoculation of 0.001 ml of throat swab fluid on antiserum agar plates and division of the results into 3 grades of intensity, showed agreement as to intensity of colonization in > 80% of repeat throat cultures. Throat swabs are probably more efficient than nasopharyngeal swabs for detecting colonization, particularly for older children. All 17 H. influenzae type b carriers found with either method were detected with throat swabs, but 6 had negative nasopharyngeal cultures; 4 of these 6 were lightly colonized older children. Colony counts were apt to be higher on plates inoculated with throat swab fluids. The frequency of pharyngeal H. influenzae type b colonization in children visiting health department clinics and pediatricians'' offices was low during the first 6 mo. of life (0.7%) but averaged 3-5% throughout the rest of childhood. Approximately 2/3 of the carriers were colonized at an intensity too low to be detected by standard laboratory techniques. No influence on colonization rates was found for sex, race, season, economic status, or common childhood infectious diseases such as coryza or otitis media.