Guides and caveats for interpreting infectious diseases data (NSW Data)
Data sources
The graphs and tables are sourced from the NSW Notifiable Diseases Database (NDD) and the NSW HIV/AIDS Database through the Health Outcomes and Statistical Toolkit (HOIST).
General guides
The graphs and tables present the number of notifications for each notifiable disease by either month or quarter of disease onset.
The graphs and tables presenting data for HIV notifications are updated quarterly for the previous full quarter and lagged by at least three to six months.
Data completeness
The completeness of case ascertainment will vary with the notification requirements of the particular disease (see Circular 2003-89), how likely the person with the illness is to present for medical care, and how 'strict' the case definition criteria are.
For example, as rabies is universally fatal without treatment, a very high proportion of rabies cases will be notified because a case will almost always be brought to medical attention. The disease is notifiable by medical practitioners, laboratories and hospitals, and there is a robust test method for diagnosis.
On the other hand, only a small proportion of influenza cases will be notified because most sufferers do not seek medical attention, are unlikely to be tested if they do present, and influenza is notifiable only by a single source (laboratories).
Timeliness
Data is current and accurate as at the displayed "Last updated" date. The number of cases reported is, however, subject to change, as cases may be entered at a later date or retracted upon further investigation. The longer the time between the period of interest and the "run-date", the more likely it is that the data are complete and the less likely they are to change.
Duplicate case reports
All databases require a process of systematic audit and duplicate removal. Duplicate removal for the HIV/AIDS Database is continuous. Duplicate removal for the NDD occurs biannually, in March and September. The March de-duplication reviews and deletes duplicates for the period 1 July to 31 December of the previous year. The September de-duplication reviews and deletes duplicates for the period 1 January to 30 June of the current year.
Graph and table contents will, therefore, alter after each duplicate check and removal procedure. Duplicate notifications (and therefore duplicates removed from the database) are most common for hepatitis B and hepatitis C infections.
Case definitions
See Australian National Notifiable Diseases Case Definitions.
Onset date
Onset date is defined as the date the patient reported that symptoms first appeared. When that date is not recorded, the onset date is defined as the date the laboratory sample was first taken to confirm diagnosis or when the case was first reported to the NSW Department of Health—whichever is earlier.
Data are presented for NSW residents only. Cases diagnosed in NSW for people who reside elsewhere are not included in the graphs and tables.
Disease specific guides
Influenza
Influenza may be categorised as Influenza-Not-Specified, Influenza-A, Influenza-B, or Influenza-A&B. Only Influenza-A and Influenza-B is reported here. Influenza-A&B is allocated to the Influenza-A category.
This web page is managed and authorised by Centre for Health Protection of the NSW Department of Health. Last updated: 27 March, 2009