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

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

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™, 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™ serotypes, there has been an increase in IPD rates due to serotypes not included in the Prevenar™ vaccine, particularly in young Aboriginal adults. 

In light of this, Prevenar™ was replaced with Prevenar-13™ on 1 July 2011, which covers 6 additional serotypes.  The findings of increasing incidence of IPD due to non-PCV7 serotypes in the West Australian Aboriginal population is consistent with national and international data.  Our data help to inform policy on optimal vaccine schedules and formulation.

Pneumococci are carried in the back of the nose of healthy as well as sick individuals.  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, thereby informing public health programs. It also gives a conservative estimate of antibiotic resistance of invasive pneumococcal strains. 

This study aims to monitor pneumococcal carriage by collecting 600 pernasal swabs from Aboriginal adults and children in urban, rural and remote areas of Western Australia annually.  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:

• describing the prevalence of upper respiratory tract (URT) carriage of other pathogens identified on primary culture;
• comparing the distribution of pneumococcal serotypes in the URT with those causing IPD in Aboriginal adults and children annually;
• storing pernasal swabs for detection of viruses by PCR to describe the prevalence of respiratory viruses; and
• investigating viral-bacterial interactions in the URT.

We recruit study participants attending health services for routine examination, immunisation or illness and also through home-visiting or community links. 

To date we have collected 1578 pernasal swabs and 58 swabs of discharge from the middle ear from a total of 559 children aged < 5 years and 1010 older children and adults.  Most of the collected swabs (1518) have been cultured. 

Recruitment has taken place in Wiluna, Kalgoorlie, Coolgardie, Laverton, Leonora, Mt Margaret, Coonana, Norseman, Roebourne, Wickham, Kununurra, Broome, Beagle Bay, Halls Creek, Carnarvon, Jigalong, Meekatharra, Burringurrah, Bunbury, Geraldton and at Aboriginal Medical Services in the Perth Metropolitan area (Perth, Armadale, Bentley, Maddington, Swan District and Kwinana).

In children under 5 years of age pneumococci were grown from 70% of pernasal swabs.  Haemophilus influenzae from 62% and Moraxella catarrhalis from 68%.  In people aged ≥5 years 35% of pernasal swabs grew pneumococci, 22% grew H. influenzae and 27% grew M. catarrhalis.  42 different serotypes have been identified.  Currently, the most common pneumococcal serotypes in children under 5 are 6A, 23F and 19A, while 6C, 16F and 6A are most common in older children and adults.

In line with data from IPD surveillance in WA Prevenar™ successfully eliminated carriage of serotypes included in this vaccine since only 12% of pneumococci were Prevenar™ serotypes.  66% of pneumococci in the URT were serotypes that are not covered by Prevenar-13™.  Ongoing surveillance of pneumococcal carriage following the change-over to Prevenar-13™ is vital for development of appropriate guidelines for Aboriginal people.

Our findings to date were presented at the Communicable Disease Control Conference in Canberra in April 2011, and the 7th World Congress for the World Society for Paediatric Infectious Diseases in November 2011 in Melbourne.

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