Do variations in pertussis notifications reflect incidence or surveillance practices? A comparison of infant notification rates and hospitalisation data in NSW

Siranda Torvaldsen, Peter McIntyre
2003 NSW Public Health Bulletin  
The incidence of pertussis cannot be directly measured; estimates are generally based on data sources such as notifications, hospitalisations and deaths. However, these data represent only a proportion of the total cases occurring in the community. The accuracy of notification data may vary between states and territories or over time due to different surveillance practices and as new diagnostic tests are introduced. These surveillance issues, and the typical three-to-five-year cycles of
more » ... s epidemics, make comparisons over time and between states and territories difficult. However, the comparisons should be more valid for hospitalisation data than for notification data, because methods of collecting hospitalisation data are likely to be more uniform. Some variation in incidence by geographical area is to be expected, depending on the timing of the last epidemic and also on geographical differences in past or present pertussis vaccination coverage. If geographical variations in pertussis notifications reflect real variations in pertussis incidence rather than reporting differences, areas with high infant (aged less than 12 months of age) notification rates would be expected to have high infant hospitalisation rates. This article describes and compares the notification and hospitalisation rates in infants for pertussis, by health area, over a period incorporating two pertussis epidemics in NSW. METHODS Medical practitioners and laboratories in NSW are required by legislation to notify the NSW Department of Health, through one of the 17 public health units, of any person who meets the case definition for pertussis. This information is then entered into the Notifiable Diseases Database (NDD). The case definition for pertussis is: 1 • isolation of Bordetella pertussis from a clinical specimen; or • elevated Bordetella pertussis specific IgA in serum or Bordetella pertussis antigen in a nasopharyngeal specimen using immunofluorescence, with a history of clinically compatible illness; or • an illness lasting two weeks or more with one of the following: paroxysms of coughing, inspiratory 'whoop' without other apparent causes, or post-tussive vomiting; or REFERENCES
doi:10.1071/nb03025 fatcat:f3lelfvo3rcgdabfeex2fjxe7y