Background

Community carriage of pneumococcal serotypes in children was assessed pre- and post-PCV10 introduction in Nepal to monitor pneumococcal vaccine impact. Molecular serotyping by microarray enabled detection of multiple-serotype carriage plus non-encapsulated pneumococcal lineages, related Streptococcus species and selected antimicrobial resistance genes.

Methods

Nasopharyngeal swabs were collected from healthy Nepalese children in 2014-15 (pre-PCV10) and 2017-18 (post-PCV10). DNA was extracted from plate sweeps of 1,241 and 1,445 swab cultures for pre- and post-vaccine periods respectively and analysed by Senti-SP molecular serotyping microarray.

Results

Comparing carriage among children pre- and post-PCV10, there was a decrease in PCV10 serotype carriage (37% vs 17%) and an increase in non-vaccine serotype carriage (67% vs 73%). There was no change for non-encapsulated pneumococcal lineages (16% vs 16%), an increase in related Streptococcal species (22% vs 25%) and an increase in detection of antimicrobial resistance genes (65% vs 74%). Multiple pneumococcal serotype carriage decreased (24% vs 16%) and multiple carriage including non-encapsulated pneumococci and related Streptococcal species also decreased (45% vs 41%).

Conclusions

Introduction of PCV10 in Nepal has resulted in a decrease in vaccine type carriage within two years. However, increases in carriage of non-vaccine types as well as antimicrobial resistance genes and related Streptococcal species were observed.

Background

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.

Methods

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).

Results

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.

Conclusions

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.

Background

Quantification of Streptococcus pneumoniae (Sp) carriage density and identification of serotypes in contacts contribute to understanding Sp transmission and thus evaluating pneumococcal conjugate vaccine impact.

Methods

266 lytA-positive nasopharyngeal samples (NPS) taken during season 1 (of 2, October-December 2017) of the Transmission of Pneumococcus (TOP) study (see abstract 715) were analysed by microarray. NPS were collected from 120 families, 2-weekly over 2 months.

Results

83/120 index children (2-year-olds) were lytA positive at baseline (visit 1): the three most common serotypes were 11A, 15B and 35F (n=83) (Graph 1).

In 17/28 families (28 index children, 45 contacts: 26 <16-year-olds and 19), index children shared ≥1 strain/serotype with ≥1 household contact.

40% (107/266) of lytA-positive NPS analysed had multiple serotypes/strains.

Sp was not detected in some lytA-positive samples but rather related streptococcal species, particularly from participants aged ≥5 years (Table 1).

Conclusions

NP carriage of the same Sp serotypes by multiple household members suggests that household Sp transmission occurs.

Multiple serotype carriage was observed in a significant proportion of participants.

Among young children, the age group most likely to transmit Sp, lytA was more predictive of true Sp infection than it was among older persons.