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Annual report National Notifiable Diseases Surveillance System, 2004
Ross River virus infection
Case defi nition – Ross River virus infection
Only confirmed cases are reported.
Confirmed case: Requires isolation of Ross
River virus, OR detection of Ross River virus by
nucleic acid testing, OR IgG seroconversion or a
significant increase in antibody level or a fourfold
or greater rise in titre to Ross River virus,
OR detection of Ross River virus-specific IgM.
There were 4,000 notifi cations of Ross River virus
(RRV) infection reported to NNDSS in 2004, which
accounts for two-thirds (67%) of the total mosquitoborne
disease notifi cations received in 2004.
The highest contributors to RRV notifications in 2004
were Queensland (45%, n=1,795), Western Australia
(27%, n=1,099), and New South Wales (18%, n=700).
The highest rates of infection were reported by the
Northern Territory (117.6 cases per 100,000 population),
Western Australia (55.4 cases per 100,000), and
Queensland (46.2 cases per 100,000 population).
The 2004 national RRV notification rate (19.9 cases
per 100,000) was the third highest RRV notification
rate reported to NNDSS since 1999.
Map 8 shows that the highest rate of RRV infection in
2004, was in the Kimberley region area of Western
Australia (202.8 cases per 100,000 population).
RRV infection notifi cations in the Northern Territory
peaked in January 2004 at 606.3 cases per 100,000
population (Figure 51). This was the highest rate
since 1999, closely resembling the RRV peak notifi
cation rate and profi le in the Northern Territory in
Figure 51. Notification rates for Ross River
virus infection, select jurisdictions, 1999 to 2004,
by month and season of onset
700
January 2001. Queensland reported the peak notifi
cation rate for RRV in March 2004 at 216.7 cases
per 100,000 population, and this was a 24 per cent
reduction from the peak notifi cation rate for April
2003 (286.3 cases per 100,000 population).
In Western Australia, a state-wide outbreak of RRV
peaked in January 2004 at 263.9 cases per 100,000
population which was the largest recorded outbreak
of RRV in Western Australia 21,22 despite early warning
through media and publicity channels. The predisposing
environmental, entomological and virological
aspects of the outbreak have been described elsewhere.
22,23
The age and sex distribution of RRV notifi cations are
shown in Figure 52. The notification rates were highest
in the 40–44 age group (38.9 cases per 100,000
population) and the female to male ratio was 1:0.9.
Figure 52. Notification rates for Ross River
virus infection, Australia, 2004, by age group
and sex
Rate per 100,000 population
45
40
35
30
25
20
15
10
5
0
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85+
Flaviviruses
Age group (years)
Male
Female
Flaviviruses are single-stranded RNA viruses, some
of which are associated with epidemic encephalitis
in various regions of the world. In Australia, the
flaviviruses of public health importance are Murray
Valley encephalitis virus (MVEV), Kunjin virus
(KUNV), Japanese encephalitis and dengue viruses.
Rate per 100,000 population
600
500
400
300
200
100
0
Jan
1999
Jul
Jan
2000
Jul
Jan
2001
Jul
Northern Territory
Queensland
Western Australia
Jan
2002
Jul
Jan
2003
Month and year of onset
Jul
Jan
2004
Jul
The Sentinel Chicken Programme is a surveillance
network involving New South Wales, the Northern
Territory, Victoria and Western Australia, and is
designed to provide early warning of increased
fl avivirus activity. 24 Antibodies to MVEV and KUNV are
detected in sentinel fl ocks located in four Australian
states. Sentinel chicken surveillance reports from
previous seasons have been published, 25–27 and
the latest report was published in CDI in 2005 as
part of the National Arbovirus and Malaria Advisory
Committee annual report, 2004–05. 28
56 CDI Vol 30 No 1 2006