Predictors of pneumococcal carriage and the effect of the 13-valent pneumococcal conjugate vaccination in the Western Australian Aboriginal population

Background: The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced to prevent invasive pneumococcal disease (IPD) in Western Australian (WA) Aboriginal people in 2001. PCV13 replaced PCV7 in July 2011, covering six additional pneumococcal serotypes; however, IPD rates remained high in Aboriginal people in WA. Upper respiratory tract pneumococcal carriage can precede IPD, and PCVs alter serotype distribution. Methods: To assess the impact of PCV13 introduction, identify emerging serotypes, and assess risk factors for carriage, nasopharyngeal swabs and information on demographic characteristics, health, medication and living conditions from Aboriginal children and adults across WA from August 2008 to November 2014 were collected. Bacteria were cultured using selective media and pneumococcal isolates were serotyped by Quellung reaction. Risk factors were analysed by multivariable logistic regression. Results: One thousand five hundred swabs pre- and 1385 swabs post-PCV13 introduction were collected. Pneumococcal carriage was detected in 66.8% of children 53.2% of 5–14 year-olds post-PCV13, compared with pre-PCV13 prevalence of 72.2% and 49.4%, respectively. The prevalence of PCV13-non-PCV7 serotypes decreased in children 13.5% pre-PCV13 to 5.8% post-PCV13 (p \u3c 0.01), and from 8.4% to 6.1% in children 5–14 years old (p \u3e 0.05). The most common serotypes post-PCV13 were 11A (prevalence 4.0%), 15B (3.5%), 16F (3.5%), and 19F (3.2%). Risk of detection of pneumococcal carriage increased until age 12 months (odds ratio [OR] 4.19, 95% confidence interval [CI] 2.39–7.33), with nasal discharge (OR 2.49 [95% CI 2.00–3.09]), residence in a remote community (OR 2.21 [95% CI 1.67–2.92]) and household crowding (OR 1.36 [95% CI 1.11–1.67]). Recent antibiotic use was negatively associated with pneumococcal carriage (OR 0.48 [95% CI 0.33–0.69]). Complete resistance to penicillin was present among isolates of serotypes 19A (6.0%), 19F (2.3%) and non-serotypeable isolates (1.9%). Serotype 23F and newly emerged serotype 7B isolates showed high rates of resistance to cotrimoxazole, erythromycin and tetracycline (86.9%, 86.9%, 82.0%, respectively for 23F, 100.0%, 100.0% and 93.3% for 7B). Conclusion: Since PCV13 replaced PCV7, carriage of PCV13-non-PCV7 serotypes decreased significantly among childrenold, those most likely to have received PCV13, and to a lesser extent in older people. Known risk factors for carriage including crowding and young age remain in the Aboriginal population

High Nasopharyngeal Carriage of Non-Vaccine Serotypes in Western Australian Aboriginal People Following 10 Years of Pneumococcal Conjugate Vaccination

BackgroundInvasive pneumococcal disease (IPD) continues to occur at high rates among Australian Aboriginal people. The seven-valent pneumococcal conjugate vaccine (7vPCV) was given in a 2-4-6-month schedule from 2001, with a 23-valent pneumococcal polysaccharide vaccine (23vPPV) booster at 18 months, and replaced with 13vPCV in July 2011. Since carriage surveillance can supplement IPD surveillance, we have monitored pneumococcal carriage in western Australia (WA) since 2008 to assess the impact of the 10-year 7vPCV program. MethodsWe collected 1,500 nasopharyngeal specimens from Aboriginal people living in varied regions of WA from August 2008 until June 2011. Specimens were cultured on selective media. Pneumococcal isolates were serotyped by the quellung reaction. ResultsStreptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were carried by 71.9%, 63.2% and 63.3% respectively of children <5 years of age, and 34.6%, 22.4% and 27.2% of people ≥5 years. Of 43 pneumococcal serotypes identified, the most common were 19A, 16F and 6C in children <5 years, and 15B, 34 and 22F in older people. 7vPCV serotypes accounted for 14.5% of all serotypeable isolates, 13vPCV for 32.4% and 23vPPV for 49.9%, with little variation across all age groups. Serotypes 1 and 12F were rarely identified, despite causing recent IPD outbreaks in WA. Complete penicillin resistance (MIC ≥2µg/ml) was found in 1.6% of serotype 19A (5.2%), 19F (4.9%) and 16F (3.2%) isolates and reduced penicillin susceptibility (MIC ≥0.125µg/ml) in 24.9% of isolates, particularly 19F (92.7%), 19A (41.3%), 16F (29.0%). Multi-resistance to cotrimoxazole, tetracycline and erythromycin was found in 83.0% of 23F isolates. Among non-serotypeable isolates 76.0% had reduced susceptibility and 4.0% showed complete resistance to penicillin.ConclusionsTen years after introduction of 7vPCV for Aboriginal Australian children, 7vPCV serotypes account for a small proportion of carried pneumococci. A large proportion of circulating serotypes are not covered by any currently licensed vaccine

Proportion of serotypeable pneumococci isolated from the nasopharynx between 2008 and 2011 that are included in 7vPCV, 13vPCV, 23vPPV, or no currently licensed vaccine, by age group.

<p>A 7vPCV program was introduced in 2001 for all Aboriginal children. Specimens were collected prior to introduction of 13vPCV in July 2011.</p

Prevalence of <i>S. pneumoniae</i> carriage in 1500 Aboriginal people (<5 years, ≥ 5 years) by Western Australian health regions.

<p>N = number of nasopharyngeal swabs collected per region for participants (< 5 years, ≥ 5 years). Overall, the prevalence of <i>S</i>. <i>pneumoniae</i> carriage was 71.9% in children < 5 years, and 34.6% in people ≥ 5 years. Specimens were collected 1 Aug 2008 - 30 June 2011.</p

Distribution of the 12 most common pneumococcal serotypes by age group.

<p>Distribution of the 12 most common pneumococcal serotypes by age group.</p