Notes on interpretation

The present report is based on 2006 'finalised' data from each state and territory. States and territories transmitted data to NNDSS on average every other day, and the final dataset for the year was agreed upon in June 2007. The finalised annual dataset represents a snap shot of the year after duplicate records and incorrect or incomplete data have been removed. Therefore, totals in this report may vary slightly from the totals reported in CDI quarterly publications.

Analyses in this report were based on the date of disease onset in an attempt to estimate disease activity within the reporting period. Where the date of onset was not known however, the date of specimen collection or date of notification, whichever was earliest, was used. As considerable time may have lapsed between onset and diagnosis dates for hepatitis B (unspecified) and hepatitis C (unspecified), for these conditions the date of diagnosis, which is the earliest of specimen, notification or notification received dates supplied, was used.

Notified cases can only represent a proportion (the 'notified fraction') of the total incidence (Figure 1) and this has to be taken into account when interpreting NNDSS data. Moreover, the notified fraction varies by disease, by jurisdiction and by time.

Figure 1. Communicable diseases notification fraction

Top of page

Methods of surveillance vary between states and territories, each having different requirements for notification by medical practitioners, laboratories and hospitals. Although there is a list of national notifiable diseases, some diseases are not yet notifiable in some jurisdictions (Table 1).

Changes in surveillance practices introduced in some jurisdictions and not in others are additional factors that make comparison of data across jurisdictions difficult. In this report, information obtained from states and territories on any changes in surveillance practices including screening practices, laboratory practices, and major disease control or prevention initiatives undertaken in 2006, was used to interpret data.

Postcode information usually reflects the residential location of the case, but this does not necessarily represent the place where the disease was acquired. As no personal identifiers are collected in NNDSS, duplication in reporting may occur if patients move from one jurisdiction to another and were notified in both.

The completenessof data in this report is summarised in Appendix 3. The case's sex was complete in 99.8% of notifications and date of birth in 100% of notifications. In 2006, indigenous status was complete in 45.8% of notifications, and varied by jurisdiction. Indigenous status was complete for 91.4% of data reported in the Northern Territory, 84.1% in South Australia and 71.6% in Western Australia. In the remaining jurisdictions, less than 54% of data were complete for indigenous status.

Data completeness on indigenous status also varied by disease; in notifications of cholera, donovanosis, leprosy, tetanus, hepatitis (NEC) and Murray Valley encephalitis virus infection, reporting on indigenous status was 100% complete. Notifications for tuberculosis (TB), syphilis less than 2 years duration, meningococcal infection and haemolytic uraemic syndrome was more than 90% complete for indigenous status, while in notifications of other diseases such as pertussis, influenza (laboratory confirmed), Barmah Forest virus infection, hepatitis C (unspecified) and Ross River virus infection, data completeness was below 40%.

Top of page

Notes on case definitions

In this report, each notifiable disease is introduced with a case definition, the 'CDNA case definition'. These case definitions were agreed upon by CDNA to be implemented nationally by January 2004.

CDNA case definitions are only intended for reporting to NNDSS. These definitions have been used by all jurisdictions from 2005 onwards. States and territories may also have case definitions which reflect their local public health needs. These may be the same as or more comprehensive than the CDNA case definitions.

Data completeness = (total notifications – missing or unknown) / total notifications x 100

Indigenous status' is a variable defined by the following values:

1=Indigenous – (Aboriginal but not Torres Strait Islander origin)

2=Indigenous – (Torres Strait Islander but not Aboriginal origin)

3=Indigenous – (Aboriginal and Torres Strait Islander origin)

4=Not indigenous – (not Aboriginal or Torres Strait Islander origin)

9=Not stated

Top of page