Dynamics of Bacterial Colonization With Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis During Symptomatic and Asymptomatic Viral Upper Respiratory Tract Infection

Abstract

Background: Virus is detected in about 80% of upper respiratory tract infections (URTIs) in children and is also detectable in the nasopharynx of 30% of asymptomatic children. The effect of asymptomatic viral infection on the dynamics of bacterial density and colonization of the nasopharynx has not been reported. The current study was performed to assess the presence and density of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the nasopharynx of 4-7-year-old children during URTI and when well.

Methods: Nasal samples were obtained during 4 surveillance periods when children were asymptomatic and whenever they had symptoms of URTI. Respiratory viruses and bacterial pathogens were identified and quantified using polymerase chain reaction.

Results: The proportion of children colonized with all 3 bacteria was higher during visits for acute URTI than during asymptomatic surveillance visits. Mean bacterial densities were significantly higher at all visits for all 3 pathogens when a virus was detected. The differences between the means were 1.0, 0.4, and 0.7 log10 colony-forming unit equivalents per milliliter for S. pneumoniae, H. influenzae, and M. catarrhalis, respectively, compared with visits in which virus was not detected. The percentage of children colonized and density were also higher at asymptomatic visits in which virus was detected than at visits in which virus was not detected.

Conclusion: The density and frequency of colonization with S. pneumoniae, H. influenzae, and M. catarrhalis in nasal wash samples increase during periods of both symptomatic and asymptomatic viral infection. Increases in bacterial colonization observed during asymptomatic viral infection were nearly the same magnitude as when children were symptomatic.

Figure 1.

Enrollment of subjects. Abbreviation: URTI, upper respiratory tract infection.

Figure 2.

Bacterial density for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis at surveillance visits (n = 847), acute upper respiratory tract infection (URTI) visits (n = 363), and recovery visits (n = 298). *P < .001 for surveillance versus acute URTI visits; †P < .01 for acute URTI versus recovery visits; ‡P = .03 for recovery versus surveillance visits. Error bars show 95% confidence intervals. Abbreviation: CFUe, colony-forming unit equivalents.

Figure 3.

Bacterial density for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis for all visits (n = 1508; A) and surveillance visits (n = 847; B) at which a virus was detected versus not detected. *P < .01 for virus detected versus not detected. Abbreviation: CFUe, colony-forming unit equivalents.

Figure 4.

Bacterial colonization rates for Streptococcus pneumoniae (A), Haemophilus influenzae (B), and Moraxella catarrhalis (C) at surveillance visits with no virus detected (SN), surveillance visits with virus detected (SV), acute upper respiratory tract infection (URTI) visits with no virus detected (AN), and acute URTI visits with virus detected (AV). *P < .05 adjusted for multiple comparisons by Tukey’s honestly significant difference method. Error bars represent 95% confidence intervals. CFUe, colony-forming unit equivalents. Abbreviations: Hi, haemophilus influenzae; Mc, moraxella catarrhalis; Sp, streptococcus pneumoniae.