The density of pneumococcal carriage provides an insight into the dynamics of transmission, colonisation and vaccine effect. We aimed to measure serotype-specific carriage density 2-3 years after 10-valent pneumococcal conjugate vaccine (PCV10) introduction, using qPCR and bacterial DNA microarray.
Nasopharyngeal swabs were collected from healthy Nepalese children from the Kathmandu Valley between April 2017 and August 2018. DNA was extracted from the swab media and qPCR performed for pneumococcal autolysin (lytA). Swab media were also plated on blood agar, incubated overnight, and plate sweeps collected. DNA was extracted from plate sweeps and molecular serotyped using the Senti-SPv1.5 microarray (BUGS Bioscience, UK).
1264 swabs were collected and analysed by both microarray and qPCR. The mean density of PCV10 serotypes was significantly higher than non-PCV10 serotypes (10^3.9 vs 10^3.4 copies/ml, p=0.004). Serotypes 1 (10^4.6 copies/ml, 95% CI 10^3.4-5.9) and 6B (10^4.6 copies/ml, 95% CI 10^3.9-5.3) had the highest mean density. Serotypes 4 (10^2.8 copies/ml, 95% CI 10^1.1-4.5) and 9N (10^2.9copies/ml, 95% CI 10^2.1-3.7) had the lowest mean carriage density.
Serotype 1, which causes the greatest proportion of invasive pneumococcal disease in this setting, was found to have the highest carriage density. Further evaluation of the PCV10 impact on carriage density is needed.