Nasopharyngeal versus oropharyngeal sampling for detection of pneumococcal carriage in adults

Several studies have shown that nasopharyngeal sampling is more sensitive than oropharyngeal sampling for the detection of pneumococcal carriage in children. The data for adults are limited and conflicting. This study was part of a larger study of pneumococcal carriage on the Navajo and White Mountain Apache Reservation following a clinical trial of a seven-valent pneumococcal conjugate vaccine. Persons aged 18 years and older living in households with children enrolled in the vaccine trial were eligible. We collected both nasopharyngeal and oropharyngeal specimens by passing a flexible calcium alginate wire swab either nasally to the posterior nasopharynx or orally to the posterior oropharynx. Swabs were placed in skim milk-tryptone-glucose-glycerin medium and frozen at -70°C. Pneumococcal isolation was performed by standard techniques. Analyses were based on specimens collected from 1,994 adults living in 1,054 households. Nasopharyngeal specimens (11.1%; 95% confidence interval [CI], 9.8 and 12.6%) were significantly more likely to grow pneumococci than were oropharyngeal specimens (5.8%; 95% CI, 4.8 to 6.9%) (P < 0.0001). Few persons had pneumococcal growth from both specimens (1.7%). Therefore, both tests together were more likely to identify pneumococcal carriage (15.2%; 95% CI, 13.7 to 16.9%) than either test alone. Although we found that nasopharyngeal sampling was more sensitive than oropharyngeal sampling, nasopharyngeal sampling alone would have underestimated the prevalence of pneumococcal carriage in this adult population. Sampling both sites may give more accurate results than sampling either site alone in studies of pneumococcal carriage in adults.