Association of Laboratory Methods, Colonization Density, and Age With Detection of Streptococcus pneumoniae in the
Catherine G Sutcliffe1,2, Lindsay R Grant2, Emily Cloessner2
1Department of Epidemiology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland.
Abstract:
Culture-based methods for detecting Streptococcus pneumoniae in the nasopharynx lack sensitivity. In this study, we aimed to compare the performance of culture and molecular methods in detecting pneumococcus in the nasopharynx of healthy individuals and to evaluate the associations of age and colonization density with detection. Between 2010 and 2012, nasopharyngeal specimens were collected from healthy individuals living on Navajo Nation and White Mountain Apache Tribal lands in the United States. Pneumococci were detected by means of broth-enrichment culture and autolysin-encoding gene (lytA) quantitative polymerase chain reaction (qPCR). Among 982 persons evaluated (median age, 18.7 years; 47% male), 35% were culture-positive and an additional 27% were qPCR-positive. Agreement between culture and qPCR was 70.9% but was higher among children (age <18 years) (75.9%-84.4%) than among adults (age ≥18 years) (61.0%-74.6%). The mean density of colonization was lower for culture-negative samples (3.14 log10 copies/mL) than for culture-positive samples (5.02 log10 copies/mL), overall and for all age groups. The percent culture-positive increased with increasing density, exceeding 80% at densities of ≥10,000 copies/mL. Mean colonization density decreased with age. Use of qPCR improved detection of pneumococcus in the nasopharynx of healthy individuals. This finding was most notable among adults, probably because of improved detection of low-density colonization.
Insights
Molecular methods like quantitative polymerase chain reaction (qPCR) significantly improve Streptococcus pneumoniae detection in the nasopharynx compared to traditional culture methods, especially in adults with low colonization density.
Area of Science:
- Microbiology
- Molecular Diagnostics
- Public Health
Background:
- Culture-based methods for detecting Streptococcus pneumoniae (pneumococcus) in the nasopharynx have known limitations in sensitivity.
- Accurate detection of pneumococcal colonization is crucial for understanding transmission and disease epidemiology.
Purpose of the Study:
- To compare the diagnostic performance of culture versus molecular methods for detecting pneumococcus in healthy individuals.
- To investigate the influence of age and bacterial colonization density on detection rates.
Main Methods:
- Nasopharyngeal specimens were collected from 982 healthy individuals between 2010-2012.
- Pneumococci were detected using both broth-enrichment culture and autolysin-encoding gene (lytA) quantitative polymerase chain reaction (qPCR).
Main Results:
- Culture detected pneumococcus in 35% of individuals, while qPCR identified an additional 27%.
- Overall agreement between methods was 70.9%, but higher in children (75.9%-84.4%) than adults (61.0%-74.6%).
- qPCR demonstrated improved detection, particularly in adults and for samples with lower colonization densities.
Conclusions:
- Quantitative polymerase chain reaction (qPCR) offers superior sensitivity for detecting nasopharyngeal pneumococcus compared to culture.
- Molecular methods are essential for accurately assessing pneumococcal colonization, especially in adults and low-density carriage states.
- Findings highlight the utility of qPCR in epidemiological studies of pneumococcal carriage.
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