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The number of cases of newly diagnosed HIV infection reported to the National HIV Database has been recognised as being affected by multiple reporting of individual cases. From April 1996, an estimate of the number of distinct cases of newly diagnosed HIV infection, adjusted for multiple reporting, has routinely been published in the Australian HIV Surveillance Report. The number of distinct HIV diagnoses was estimated using a statistical algorithm based on the reported birth date of each case.¹ Multiple reporting of cases of HIV infection was estimated as occurring most frequently in New South Wales.² A substantial change in the number of cases of HIV infection diagnosed in New South Wales is now being reported.

Prior to the establishment of national surveillance for cases of newly diagnosed HIV infection, each State and Territory health authority independently developed procedures for monitoring HIV diagnoses. In some health jurisdictions, the full name of people with newly diagnosed HIV infection was sought whereas in other jurisdictions, no identifying information was collected.

From July 1990, cases of newly diagnosed HIV infection were reported nationally with the person's date of birth and sex only.³ National reporting of cases with name code (based on the first two letters of the family name and the first two letters of the given name) was introduced in January 1993, to facilitate identification and removal of duplicate diagnoses.

Partly because of the limited identifying information originally sought on cases of newly diagnosed HIV infection, and partly due to confidentiality concerns early in the HIV epidemic, HIV diagnoses in New South Wales have included more than 3,500 records without identifying information including name code and date of birth. Because the majority of these cases were newly diagnosed in the mid 1980s, it is likely that these cases have been, or will again be, diagnosed and notified to the National HIV Database and not be recognised as duplicate notifications. For these reasons, records of HIV diagnosis in New South Wales without name code and date of birth have been removed from the National HIV Database.

The New South Wales Health Department also indicated that a large number of records of HIV diagnosis had not been notified to the National HIV Database as they had been reported as previously diagnosed. These records were matched on birth date with records of HIV diagnosis reported to the National HIV Database to identify those records with newly available dates of birth or a previously available date of birth and newly available name codes. A total of 1,165 records of HIV diagnosis reported as previously diagnosed have now been added to the National HIV Database, including 976 records with a newly available date of birth.

The net effect of these changes to the National HIV Database has been to reduce the number of cases of newly diagnosed HIV infection reported by the end of 1997, from 21,080 to 18,674 in Australia as a whole, and from 13,282 to 10,899 in New South Wales. The estimated number of distinct HIV diagnoses has, however, remained broadly unchanged. Prior to the changes being made, 16,870 distinct cases of HIV infection (plausible range 15,940 to 17,810) were estimated as having been diagnosed in Australia compared to 16,030 cases (plausible range 15,620 to 16,440) after the changes had been made. The estimate of the number of distinct HIV diagnoses in New South Wales has been revised from 10,050 cases (range 9,300 to 10,800) to 9,570 cases (range 9,280 to 9,870).

These changes to the National HIV Database reduce the uncertainty surrounding the estimate of the number of distinct HIV diagnoses. Furthermore, the newly available information on name code and date of birth allows more complete identification of cases of repeat diagnosis, especially between State and Territory health authorities, leading to an ongoing improvement in monitoring the extent of diagnosed HIV infection in Australia.

References

1. Law MG, McDonald AM and Kaldor JM. Estimation of cumulative HIV incidence in Australia, based on national case reporting. Aust NZ J Public Health 1996;20:215-217.

2. National Centre in HIV Epidemiology and Clinical Research (editor). HIV/AIDS and related diseases in Australia Annual Surveillance Report 1997. National Centre in HIV Epidemiology and Clinical Research, Sydney. 1997.

3. McDonald AM, Crofts N, Blumer CE, Gertig DM, Patten JJ, Roberts M, et al. The pattern of diagnosed HIV infection in Australia, 1984 - 1992. AIDS 1994;8:13-519.

HIV and AIDS diagnoses for the current reporting period are presented on page 169.

This article was published in Communicable Diseases Intelligence Vol 22 No 8, 6 August 1998.