Monitoring carriage of Streptococcus pneumoniae among Aboriginal children and adults in Western Australia

Deborah Lehmann, Anke Hoskins, Deirdre Collins, Janice Lim, Kalpani Senasinghe in collaboration with Jacinta Bowman, Natalie Thomsen, Tom Riley, Carolien Giele, Paul Effler, Amanda Leach, Peter Richmond

 

Streptococcus pneumoniae (pneumococcus) can cause middle ear infections and invasive pneumococcal disease (IPD) resulting in meningitis, pneumonia and septicaemia (blood poisoning).

 

The Australian Aboriginal population has among the highest reported IPD rates worldwide.  The existence of over 90 known types (serotypes) of pneumococci increases the challenge of prevention.

 

A pneumococcal conjugate vaccine (Prevenar-7™, PCV7 ) covering the 7 most common serotypes causing IPD in a 2-4-6-month schedule and an 18-month booster with a pneumococcal polysaccharide vaccine (Pneumovax™) covering 23 serotypes have been offered to Aboriginal children since 2001. Pneumovax™ is also offered to adults.

 

While there has been a marked reduction in IPD due to the near elimination of Prevenar-7™ serotypes, there has been an increase in IPD rates, particularly in young Aboriginal adults, due to serotypes not included in the vaccine. In light of this, Prevenar-7™ was replaced with Prevenar-13™ on 1 July 2011, which covers 6 additional serotypes.


Pneumococci are carried in the back of the nose of healthy as well as sick individuals and the acquisition of pneumococci is prerequisite to develop disease. Surveillance of pneumococcal carriage offers important complementary information to data on IPD since it can quickly provide a large amount of information on serotypes circulating in the population. It also gives a conservative estimate of antibiotic resistance of invasive pneumococcal strains.


This study aims to monitor the impact of different versions of PCV on pneumococcal carriage by collecting pernasal swabs opportunistically from Aboriginal adults and children in urban, rural and remote areas of Western Australia. We also collect ear swabs from children with middle ear discharge and data on vaccination status of children in the study.

Other study aims include:

  1. Describing the prevalence of upper respiratory tract (URT) carriage of other pathogens identified on primary culture
  2. Comparing the distribution of pneumococcal serotypes in the URT with those causing IPD in Aboriginal adults and children annually
  3. Monitoring antibiotic resistance pattern of pneumococci
  4. Storing pernasal swabs for detection of viruses by PCR to describe the prevalence of respiratory viruses and
  5. Investigating viral-bacterial interactions in the URT.
  6. To date we have collected ~2200 pernasal swabs and 50 swabs of discharge from the middle ear.


Pneumococcal carriage rates remain high in young children, being highest in the 6-23 month age group (~80%).  Approximately 12% of young adults and 10% of people over 65 years of age carried pneumococci.

 

In children under 5 years of age nontypeable Haemophilus influenzae was grown from 62% and Moraxella catarrhalis from 68% of pernasal swabs. In people aged ≥5 years 22% grew nontypeable Haemophilus influenzae and 27% grew Moraxella catarrhalis. Thirty four different pneumococcal serotypes were carried in children <5 years of age and 37 different serotypes have been identified in people ≥5 years.

 

Currently, the most common pneumococcal serotypes in children <5 years of age are 19F, 6C and 16F while 19F, 6A/6C and 10A are most common in older children and adults. There has been some reduction in carriage of serotypes included Prevenar-13™ since its introduction 18months ago but the proportion of serotypes identified in the URT which are not covered by Prevenar-13™ remains high (~70%). Surveillance is ongoing.


Our findings were presented at the 8th International Symposium on Pneumococci and Pneumococcal Diseases (ISPPD8) in March 2012. A manuscript describing URT carriage until July 2011 is in advanced draft stage.

 

Funders of the project: Western Australian Department of Health through the Collaboration for Applied Research and Evaluation (CARE) and NHMRC Project Grant #545232 (a collaboration with the Menzies School of Health Research)

Team Members

Deborah Lehmann, Anke Hoskins, Deirdre Collins, Janice Lim, Kalpani Senasinghe in collaboration with Jacinta Bowman, Natalie Thomsen, Tom Riley, Carolien Giele, Paul Effler, Amanda Leach, Peter Richmond

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