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Dynamics of Colonization of Streptococcus pneumoniae Strains in Healthy Peruvian Children
Kristin N Nelson1, Carlos G Grijalva2, Sopio Chochua1
1Department of Epidemiology, Emory University Rollins School of Public Health, Atlanta, Georgia.
Insights
The 7-valent pneumococcal vaccine (PCV7) did not change overall Streptococcus pneumoniae (Spn) carriage in Peruvian children. However, PCV7 introduction shifted serotype-specific carriage rates and longitudinal patterns in young children.
Area of Science:
- Pediatric infectious diseases
- Vaccinology
- Microbiology
Background:
- Asymptomatic carriage of Streptococcus pneumoniae (Spn) is the initial step in disease development.
- The 7-valent pneumococcal vaccine (PCV7) was introduced to reduce Spn-related illnesses.
- Understanding Spn carriage dynamics is crucial for assessing vaccine impact.
Purpose of the Study:
- To evaluate the impact of PCV7 introduction on Spn carriage patterns in Peruvian children.
- To analyze changes in Spn serotype distribution and carriage duration before and after PCV7 vaccination.
- To identify specific Spn serotypes acting as 'persisters' or 'recolonizers' post-vaccination.
Main Methods:
- Prospective cohort study of children under 3 years old in Peru.
- Monthly nasopharyngeal sampling and Spn isolate serotyping using Quellung reactions.
- Quantitative PCR to determine bacterial density; analysis of carriage rates, serotype counts, and density over time.
- Identification of 'persister' and 'recolonizer' serotypes based on longitudinal detection patterns.
Main Results:
- Overall Spn carriage prevalence remained high (92% in 2009, 89% in 2011) and carriage rates were similar (9.03 vs. 9.04 detections/person-year).
- Before PCV7 (2009), serotype 23F was a 'persister,' while 6A, 15B, and 19A were 'recolonizers.'
- After PCV7 introduction (2011), serotypes 6B and 7C became 'persisters,' and serotype 13 was a frequent 'recolonizer.'
Conclusions:
- PCV7 introduction did not significantly alter overall Spn carriage prevalence in young Peruvian children.
- Significant shifts in serotype-specific carriage rates and longitudinal patterns were observed post-PCV7 introduction.
- The study highlights the dynamic nature of Spn carriage and the emergence of different serotypes following vaccination.
Background:
Although asymptomatic carriage of Streptococcus pneumoniae (Spn) is common, acquisition of the bacteria is the first step in disease pathogenesis. We examined the effect of introduction of the 7-valent pneumococcal vaccine on Spn carriage patterns in a cohort of Peruvian children.
Methods:
We used data from a prospective cohort study that collected monthly nasopharyngeal samples from children under 3 years of age. Spn isolates were serotyped using Quellung reactions, and bacterial density was determined by quantitative polymerase chain reaction. Changes in Spn carriage patterns, including the rate of carriage and number and density of serotypes carried over time, were evaluated before (2009) and after widespread vaccination with PCV7 (2011). Using all pneumococcal detections from each child and year, we identified serotypes that were present both at first and last detection as "persisters" and serotypes that replaced a different earlier type and were detected last as "recolonizers."
Results:
Ninety-two percent (467/506) of children in 2009 and 89% (451/509) in 2011 carried Spn at least once. In 2009 and 2011, rates of carriage were 9.03 and 9.04 Spn detections per person-year, respectively. In 2009, 23F, a serotype included in PCV7, was the only type identified as a persister and 6A, 15B, and 19A were identified as recolonizer serotypes. In 2011, 6B and 7C were persister serotypes and 13 was a frequent recolonizer serotype.
Conclusions:
Overall Spn carriage among children under 3 in Peru was similar before and after introduction of PCV7; however, serotype-specific rates and longitudinal carriage patterns have shifted.
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