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National Influenza Surveillance Scheme

Based on Annual report of the National Influenza Surveillance Scheme 2000, (Commun Dis Intell 2000;25:107).

In 2000, influenza surveillance in Australia was based on three systems: laboratory diagnosis by virus isolation and serology from laboratories participating in LabVISE, consultation rates for clinically diagnosed influenza illness by sentinel general practitioners; and the absenteeism data of workers from a national employer. Sentinel general practice schemes were both State-based (in New South Wales, Victoria and the Northern Territory) and national through reporting to the Australian Sentinel Practice Research Network.

In 2000, participating laboratories of the LabVISE scheme reported a total of 1,916 laboratory isolations of influenza. These included 1,366 reports of influenza A and 550 reports of influenza B. The ratio of influenza A to B was 2.5:1. Total influenza reports showed a low level of activity until mid-June when there was an increase in reports to approximately 50 per week, followed by a major peak in mid-September, then a decline to baseline by late November. There were few temporal differences in the peaks of influenza A compared with influenza B activity through the year. The peak of influenza activity in 2000 was significantly later in the year than in 1999. The pattern in 2000 closely resembled that in 1997, when there was also a larger proportion of influenza B isolates (influenza A to B ratio of 1.5:1) and a later peak in disease reporting. The overall male to female ratio for influenza in 2000 was 1.2:1. The age and sex rates were highest among infants and children aged less than 5 years, with a second peak among men aged 70 years or more and women aged 75 years or more.

The Northern Territory Tropical Influenza Surveillance scheme data showed two peaks of influenza activity in March and October. The ASPREN data and that of New South Wales and Victorian sentinel schemes all showed a single peak in reporting in the week ending 17 September. Comparison of the ASPREN and LabVISE reports showed a similar pattern of activity, with the peak in laboratory reports one week later than that from general practitioner surveillance.

The WHO Collaborating Centre for Reference and Research on Influenzareceived a total of 1,116 influenza isolates of which 922 (83%) were suitable for analysis. Of these, 518 (56%) were influenza A (H3N2) subtype, 262 (28%) were influenza B and the remaining 142 (16%) were influenza A (H1N1) subtype.

The influenza A (H1N1) isolates were predominantly (73%) A/New Caledonia/20/99-like viruses with only 39 isolates characterised as A/Bayern/7/95-like. These two separate lineages of viruses have co-circulated in Australia for some time. Although 3 sporadic isolates of the A/New Caledonia lineage were isolated in 1999, this is the first year in which viruses of the lineage have been isolated in significant numbers in Australia. All but one of the 39 A/Bayern/7/95-like isolates came from an outbreak in South Australia.

The majority of the influenza A(H3N2) isolates (94%) were most closely related to the reference strain A/Moscow/10/99 and vaccine strain A/Panama/2007/99 and were distinguishable from the previous prototype and vaccine strain A/Sydney/5/97. Nevertheless, serological studies demonstrated that vaccines containing an A/Sydney/5/97-like strain used in the Australian 2000 Winter produced similar antibody responses to the Australian 2000 A (H3N2) isolates as vaccines containing an A/Moscow/10/99-like strain used in the 2000/2001 Northern Hemisphere Winter. Thus while some antigenic heterogeneity was observed in the influenza A (H3N2) isolates there was no evidence of significant antigenic drift beyond the A/Moscow/10/99 reference strain.

Influenza B strains isolated during the 2000 season showed a progressive drift away from the B/Beijing/184/93 strain. The majority (64%) were most closely related antigenitically to the new reference strain B/Sichuan/379/99.

In 1999/2000, there were a total of 2,591 admissions to Australian hospitals for influenza/pneumonia (Source: National Hospital Morbidity Database, 1990-2000: AIHW). Influenza virus was identified in 673 of these were cases. Altogether, influenza was responsible for 4,583 hospital patient days in 1999/2000.


This article was published in Communicable Diseases Intelligence Volume 26, No 2, June 2002