ABSTRACT
Pneumococcal disease is a major contributor to global childhood morbidity and mortality and is more common in low- and middle-income countries (LMICs) than in high-income countries. Pneumococcal carriage is a prerequisite for pneumococcal disease. Pneumococcal conjugate vaccine reduces vaccine-type carriage and disease. However, pneumococcal carriage and disease persist, and it is important to identify other potentially modifiable factors associated with pneumococcal carriage and determine if risk factors differ between low, middle, and high-income countries. This information may help inform pneumococcal disease prevention programs. This systematic literature review describes factors associated with pneumococcal carriage stratified by country income status and summarises pneumococcal carriage rates for included studies. We undertook a systematic search of English-language pneumococcal nasopharyngeal carriage studies up to 30th June 2021. Peer-reviewed studies reporting factors associated with overall pneumococcal nasopharyngeal carriage in healthy, community-based study populations were eligible for inclusion. Two researchers independently reviewed studies to determine eligibility. Results are presented as narrative summaries. This review is registered with PROSPERO, CRD42020186914. Eighty-two studies were included, and 46 (56%) were conducted in LMICs. There was heterogeneity in the factors assessed in each study. Factors positively associated with pneumococcal carriage in all income classification were young age, ethnicity, symptoms of respiratory tract infection, childcare attendance, living with young children, poverty, exposure to smoke, season, and co-colonisation with other pathogens. Breastfeeding and antibiotic use were protective against carriage in all income classifications. Median (interquartile range) pneumococcal carriage rates differed by income classification, ranging from 51% (19.3-70.2%), 38.5% (19.3-51.6%), 31.5% (19.0-51.0%), 28.5% (16.8-35.4%), (P = 0.005) in low-, lower-middle, upper-middle, and high-income classifications, respectively. Our findings suggest that where measured, factors associated with pneumococcal nasopharyngeal carriage are similar across income classifications, despite the highest pneumococcal carriage rates being in low-income classifications. Reducing viral transmission through vaccination and public health interventions to address social determinants of health would play an important role.
ABSTRACT
Importance: Pneumococcal nasopharyngeal carriage is a prerequisite for pneumococcal disease. The main transmission route is from toddlers, who commonly carry pneumococci. However, neonatal pneumococcal disease case reports suggest that vertical pneumococcal transmission may also occur. Objective: To describe and compare pneumococcal nasopharyngeal carriage and density by infant mode of delivery in young Fijian infants. Design, Setting, and Participants: Annual cross-sectional surveys were performed in Suva, Fiji, before the introduction of 10-valent pneumococcal conjugate vaccine (PCV10), from September 14 to December 20, 2012, and after PCV10 was introduced, from July 11 to November 19, 2013; July 15 to December 9, 2014; and August 13 to November 19, 2015. Caregivers of 2006 infants aged 5 to 8 weeks participated in the surveys. Statistical analysis was performed from May 24, 2018, to August 12, 2019. Exposures: Caregivers provided data on infant mode of delivery and demographics via interviewer-led survey. Main Outcomes and Measures: Pneumococci in swab samples were detected and quantified by lytA quantitative polymerase chain reaction with molecular serotyping by microarray. Pneumococci were categorized as PCV10 or non-PCV10 serotypes. Results: Of the 2006 infants (976 girls and 1030 boys; mean [SD] age, 6.1 [0.02] weeks]), 1742 (86.8%) were born vaginally and 264 were born by cesarean delivery. Infants delivered vaginally, compared with those born by cesarean delivery, had a higher prevalence of overall pneumococcal nasopharyngeal carriage (470 of 1722 [27.3%; 95% CI, 25.2%-29.4%] vs 47 of 260 [18.1%; 95% CI, 13.6%-23.3%]; P = .002), PCV10 carriage (113 of 1698 [6.7%; 95% CI, 5.5%-7.9%] vs 8 of 256 [3.1%; 95% CI, 1.4%-6.1%]; P = .03), and non-PCV10 carriage (355 of 1698 [20.9%; 95% CI, 19.0%-22.9%] vs 38 of 256 [14.8%; 95% CI, 10.7%-19.8%]; P = .02), and had higher median densities of overall pneumococci (4.9 log10 genome equivalents [GE]/mL [interquartile range, 4.8-5.0 log10 GE/mL] vs 4.5 log10 GE/mL [interquartile range, 4.1-4.6 log10 GE/mL]; P = .01) and non-PCV10 pneumococci (4.9 log10 GE/mL [interquartile range, 4.7-5.0 log10 GE/mL] vs 4.4 log10 GE/mL [interquartile range, 4.0-4.7 log10 GE/mL]; P = .01). Vaginal delivery was associated with overall (adjusted odds ratio, 1.57 [95% CI, 1.10-2.23]; P = .01) and non-PCV10 (adjusted odds ratio, 1.49 [95% CI, 1.01-2.20]; P = .04]) pneumococcal nasopharyngeal carriage. Vaginal delivery was not associated with PCV10 carriage (adjusted odds ratio, 1.67 [95% CI, 0.80-3.51]; P = .17). After adjustment, vaginal delivery was not associated with density. Conclusions and Relevance: Pneumococcal nasopharyngeal carriage prevalence and density were higher in infants delivered vaginally compared with those delivered by cesarean birth. After adjustment, vaginal delivery was associated with pneumococcal carriage. Differences in carriage by mode of delivery may be due to differential exposure to the vaginal microbiota during delivery and the effect of intrapartum antibiotics during cesarean delivery on the infant microbiome. Our findings also raise the hypothesis that vertical transmission may contribute to pneumococcal acquisition.
