Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus are commonly carried in the nasopharynx of young children, and have been speculated to interact with each other. Although earlier studies used cultures alone to assess these interactions, the addition of real-time quantitative polymerase chain reaction (qPCR) provides further insight into these interactions. We compared results of culture and qPCR for the detection of these 3 bacteria in 446 nasopharynx samples collected from 360 healthy young children in a prospective cohort study in the Peruvian Andes. Patterns of concurrent bacterial colonization were studied using repeated measures logistic regression models with generalized estimating equations. Spearman correlation coefficients were used to assess correlations among bacterial densities. At a bacterial density <105 colony forming units/mL measured by qPCR, culture detected significantly less carriers (P < 0.0001) for all 3 pathogens, than at a bacterial density >105 colony forming units/mL. In addition, there was a positive association between S. pneumoniae and H. influenzae colonization measured by both culture (odds ratio [OR] 3.11–3.17, P < 0.001) and qPCR (OR 1.95–1.97, P < 0.01). The densities of S. pneumoniae and H. influenzae, measured by qPCR, were positively correlated (correlation coefficient 0.32, P < 0.001). A negative association was found between the presence of S. pneumoniae and Staphylococcus aureus in carriage with both culture (OR 0.45, P = 0.024) and qPCR (OR 0.61, P < 0.05). The impact of density on detection by culture and the observed density-related interactions support use of qPCR in additional studies to examine vaccine effects on diverse bacterial species.
From the * Department of Epidemiology, Rollins School of Public Health, Emory University; † Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA; Departments of ‡ Preventive Medicine; § Pediatrics (Division of Infectious Diseases); ¶ Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN; ∥ Instituto de Investigación Nutricional, Lima, Peru; and **University of Basel, Basel, Switzerland.
Accepted for publication August 15, 2012.
This study was supported in part by Vanderbilt University, the Vanderbilt CTSA grant UL1 RR024975-01 from National Center for Research Resources /National Institutes of Health and Pfizer (New York, NY; IIR WS1898786[0887X1-4492]). In addition to an institutional grant from Pfizer, KPK has received consulted for Pfizer vaccines, GlaxoSmithKline (Research Triangle Park, NC), Novartis (New York, NY), Sanofi (Bridgewater, NJ) and Merck (Whitehouse Station, NJ), and he has received speaking fees from Pfizer and GlaxoSmithKline. MRG has consulted for Novavax (Rockville, MD); CGG has consulted for GlaxoSmithKline; JVW has consulted for Quidel (Santa Clara, CA) and MedImmune (Gaithersburg, MD).
The authors have no other funding or conflicts of interest to disclose.
Address for correspondence: Keith P. Klugman, MD, PhD, Rollins School of Public Health, 1518 Clifton Road Atlanta, GA 30322. E-mail: email@example.com.