• Marlena C Kaczmarek, Lisa Valenti, Heath A Kelly, Robert S Ware, Helena C Britt, and Stephen B Lambert.
• Queensland Children's Medical Research Institute, Brisbane, QLD, Australia. marlena.kaczmarek@mh.org.au
• Med. J. Aust.. 2013 Jun 17;198(11):624-8.

ObjectiveTo better understand the role that diagnostic test-ordering behaviour of general practitioners has on current pertussis epidemiology in Australia.Design And SettingAnalysis of Australian general practice encounter data (from the Bettering the Evaluation and Care of Health [BEACH] program) on 13 "pertussis-related problem" (PRP) codes that were most likely to result in a pertussis laboratory test request and Australian pertussis notifications data (from the National Notifiable Diseases Surveillance System [NNDSS]) for the period April 2000 to March 2011.Main Outcome MeasuresThe change in the proportion of PRP general practice encounters with a pertussis test request between 2000 and 2011, and the change in national pertussis notifications over the same period.ResultsThe proportion of PRP encounters resulting in a pertussis test request increased from 0.25% between April 2000 and March 2004 to 1.71% between April 2010 and March 2011 (odds ratio, 7.0; 95% CI, 5.5-8.8). The BEACH data on pertussis testing and NNDSS data on pertussis notifications were highly correlated (r = 0.99), and the notification data mirrored the likelihood of a pertussis test request in general practice. The proportion of NNDSS pertussis notifications with a polymerase chain reaction (PCR)-confirmed diagnosis increased from 16.3% between April 2000 and March 2004 to 65.3% between April 2010 and March 2011.ConclusionAn increase in pertussis testing following recognition of early epidemic cases may have led to identification of previously undetected infections, resulting in a further increase in notified disease and awareness among GPs. The changing likelihood of being tested may also be due to expanding availability and use of PCR testing in Australia.

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