Australia’s notifiable disease status, 2013: Annual report of the National Notifiable Diseases Surveillance System: Part 7

The National Notifiable Diseases Surveillance System monitors the incidence of an agreed list of communicable diseases in Australia. This report analyses notifications during 2013.

Page last updated: 16 October 2015

Results - Part 2 continued

Vectorborne diseases

Overview

Vectorborne diseases are infections transmitted by arthropods such as mosquitoes and ticks. A vectorborne disease may involve a simple transfer via the arthropod, or, may involve replication of the disease-causing organism in the vector.21 Vectorborne diseases of public health importance in Australia listed in this chapter are: arbovirus not elsewhere classified (NEC); Barmah Forest virus (BFV) infection; dengue virus (DENV) infection; Japanese encephalitis virus (JEV) infection; Kunjin virus (KUNV) infection, malaria, Murray Valley encephalitis virus (MVEV) infection and Ross River virus (RRV) infection. Some vectorborne diseases, including yellow fever infection, plague and certain viral haemorrhagic fevers, are listed under quarantinable diseases. The National Arbovirus and Malaria Advisory Committee provide expert technical advice on vectorborne diseases to the Australian Health Protection Principal Committee through CDNA.

Alphaviruses

Viruses in the genus Alphavirus that are notifiable in Australia are BFV and RRV. These viruses are unique to the Australasian region.87 Infection can cause a clinical illness, which is characterised by fever, rash and polyarthritis. The viruses are transmitted by numerous species of mosquito that breed in diverse environments.88 The alphavirus chikungunya was not nationally notifiable in 2013, and thus not included in this annual report. However, it is notifiable in all states and territories except the Australian Capital Territory, and states and territories send information about cases to the Commonwealth for national collation and analysis.89,90 Chikungunya virus infection was made nationally notifiable in January 2015.

The national case definitions for RRV and BFV require only a single IgM positive test to 1 virus, in the absence of IgM to the other.18 False positive IgM diagnoses for BFV in particular are a known issue, thus it is unclear what proportion of notifications represent true cases.

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Barmah Forest virus infection
  • There was a dramatic increase in case numbers and rates thought to be due to an increase in false positive notifications.
  • Females were disproportionately affected in 2013, and the most affected age groups were younger than in previous years.
Epidemiological situation in 2013

In 2013, there were 4,239 notifications of BFV infection, for a rate of 18.3 per 100,000 population. This compares with a 5-year mean of 1,723 notifications and a 5-year mean rate of 7.8 per 100,000. The number of notifications of Barmah Forest virus increased sharply from October 2012 (Figure 74). This increase continued into late 2013 and beyond for some jurisdictions. The increase was considered likely to have been due to a high rate of false positive IgM test results from the use of a commercial test kit in private laboratories, and resulted in a recall of the affected kits in September 2013.91

Figure 74: Notified cases of Barmah Forest virus infection, Australia, 2008 to 2013, by year and month and state or territory

bar chart. A link to a text description follows.

Text version of Figure 74 (TXT 1 KB)

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Geographic description

More than half of all BFV notifications in 2013 were from Queensland (52%, 2,224/4,239) and population rates were highest in the Northern Territory (167.9 per 100,000), Queensland (47.8 per 100,000) and Western Australia (40.6 per 100,000). All of these rates were more than double the 5-year mean, with rate ratios of 4.5, 2.2 and 6.4 respectively for 2013 compared with the 5-year mean rate. In New South Wales, South Australia and Victoria, rates were similar to the 5-year mean.

Age and sex distribution

In 2013, BFV infection was most frequently reported in people aged between 10 and 54 years (median 46 years, range 0–92 years), in contrast to previous years where the age groups most affected were middle aged and older adults. In 2013, age and sex specific rates were highest among females in the 35–54 years age group, and the next highest rate was among females aged 15–34 years (Figure 75). In 2013, rates were much higher in females overall than in males (21.9 and 14.7 per 100,000 respectively) with a rate ratio of 1.5:1. By contrast, between 2008 and 2012, rates in females were marginally lower than in males (7.6 and 8.0 per 100,000 respectively) with a rate ratio of 0.9:1.

Figure 75: Notification rate for Barmah Forest virus, Australia, 2013 and 2008 to 2012, by age group and sex (n=12,852)

line chart. A link to a text description follows.

Text version of Figure 75 (TXT 1 KB)

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Seasonality

Peak incidence of BFV could be expected to occur during the warmer months (or during wetter months in northern areas of Australia) when mosquito numbers are high. However, seasonality of notifications is less marked than expected (Figure 75), and a high proportion of inter-seasonal notifications are thought to be due to false positive diagnoses. Peak notification of BFV in 2013 was between January and April, with 47% (1,997/4,239) of notifications being during this period, similar to between 2008 and 2012 (46% ,3,925/8,616). The increase from October 2012 that was thought to be due to false positive notifications was earlier than the expected seasonal increase.

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Discussion

The dramatic increase in counts and rates in 2013 disproportionately affected females, with much higher rates in females and in younger age groups than observed in previous years. The CDNA surveillance case definition for BFV92 in 2013 allowed for confirmation based on a single positive IgM, in the absence of IgM to other alphaviruses. Not all jurisdictions reported increases, and this may in part be due to differences in laboratory and notification practices. South Australia requires seroconversion to BFV, and in Victoria, metropolitan cases without any travel to non-metropolitan areas require evidence of seroconversion.

Given the dramatic increase in notifications in late 2012 and 2013, the possibility of false positive diagnoses based on a single positive IgM, and also the difference in surveillance and notification practices, CDNA has referred the BFV surveillance case definition to the CDWG for review.

Ross River virus infection
  • Notifications were similar to the 5-year mean.
Epidemiological situation in 2013

In 2013, there were 4,308 notifications of RRV, which was a rate of 18.6 per 100,000. This compares with a 5-year mean of 5,061 cases and a 5-year mean rate of 23.0 per 100,000.

Geographic description

In 2013, nearly half of all RRV infections were from Queensland (41% of all cases, 1,787/4,308, for a rate of 38.4 cases per 100,000), but population rates were highest in the Northern Territory (124.4 per 100,000) and Western Australia (54.3 per 100,000).

Age and sex distribution

RRV was most frequently reported in adults aged in their 30s or 40s (median 44 years, range 0–95 years), similar to previous years. Rates were similar in females and males (rates of 19.7 and 17.5 per 100,000 respectively) with a ratio of 1.1:1, similar to previous years. In 2013, age specific rates were highest among the 35–49 year age range for females, and the 35–44 year age range for males (Figure 76).

Figure 76: Notification rates for Ross River virus, 2013, by age group and sex (n=4,308)

line chart. A link to a text description follows.

Text version of Figure 76 (TXT 1 KB)

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Seasonality

Peak notification for RRV in 2013 was between January and April, and 44% of cases were diagnosed during these months (Figure 77). Between 2008 and 2012, 58% of notifications were between January and April, indicating that in 2013, the proportion of inter-seasonal notifications was higher than in previous years.

Figure 77: Notified cases of Ross River virus, Australia, 2008 to 2013, by year and month and state or territory

bar chart. A link to a text description follows.

Text version of Figure 77 (TXT 1 KB)

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Flaviviruses

In Australia, flavivirus infections of particular public health importance are DENV, KUNV, MVEV and JEV. Yellow fever is reported under Quarantinable diseases. These infections are nationally notifiable. No specific treatment is available for these diseases and care is largely supportive. A vaccine is available to prevent JEV infection50 but there are no vaccines currently for DENV, MVEV or KUNV infection.

Infection with MVEV, KUNV or JEV is usually asymptomatic or produces a non-specific illness, but a small percentage of cases progress to encephalomyelitis of variable severity. Culex annulirostris is the major vector of MVEV, JEV and KUNV. DENV has 4 serotypes, each containing numerous genotypes. The serotypes isolated from returning travellers (and thus involved in local outbreaks) vary by year and geographical region. Infection with 1 serotype probably confers lifelong immunity to that serotype,21 but subsequent infection with a different serotype is 1 factor thought to increase the risk of severe outcomes, along with the infecting serotype and genotype, and host factors.21,93–95 The clinical illness is characterised by mild to severe febrile illness with fever, headache, muscle and joint pain and sometimes a rash. A minority of cases progress to severe dengue with haemorrhage and shock. Aedes aegypti is the major vector of DENV in Australia.

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Arbovirus NEC
  • 21 cases of arbovirus (NEC) were notified in 2013.

Unspecified flavivirus infections are reported under arbovirus NEC. From 2015, arbovirus NEC has been renamed flavivirus NEC.

Epidemiological situation in 2013

In 2013, there were 21 notifications of arbovirus (NEC) compared with an average of 11.8 during the previous 5 years. All but one of these notifications was from Queensland. These notifications comprised Alfuy (1 case), Kokobera (5 cases) and Zika (1 case), and the infecting flavivirus was unknown or not supplied for a further 14 cases (Table 16).

Table 16: Notified cases of arbovirus NEC, Australia, 2013
State or territory Country of acquisition Organism Age group Sex
Qld
Unknown Kokobera
20–24
Female
Qld
Unknown Kokobera
35–39
Female
Qld
Unknown Kokobera
55–59
Male
Qld
Unknown Kokobera
75–79
Male
Qld
Unknown Untyped
25–29
Male
Qld
Unknown Untyped
50–54
Female
Qld
Unknown Untyped
55–59
Female
Qld
Unknown Untyped
60–64
Male
Qld
Australia Kokobera
15–19
Female
Qld
Papua New Guinea Untyped
20–24
Female
Qld
Papua New Guinea Untyped
35–39
Male
Qld
Vanuatu Alfuy
35–39
Female
Qld
Democratic Republic of Korea (North Korea) Untyped
45–49
Male
Qld
Democratic Republic of Korea (North Korea) Untyped
50–54
Male
Qld
Republic of Korea (South Korea) Untyped
30–34
Male
Qld
Indonesia Untyped
20–24
Male
Qld
Indonesia Untyped
45–49
Male
Qld
Indonesia Untyped
50–54
Male
Qld
Philippines Untyped
40–44
Female
Qld
India Untyped
45–49
Female
NT
Indonesia Zika
25–29
Male

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Information about the country of acquisition was available for 62% of cases (13/21), and 12 of these were acquired overseas.

The median age of cases was 43 years (range 19–76 years). Nine cases were female and 12 cases were male.

Dengue virus infection
  • There was a continuing increase in the number of overseas acquired cases.
  • 235 cases were acquired in Australia in 2013, including 2 acquired in Western Australia.

Local transmission of dengue in Australia is normally restricted to areas of northern Queensland where the key mosquito vector, Ae. aegypti is present.96 Dengue is not endemic in North Queensland, but local transmission can occur upon introduction of the virus to the mosquito vector by a viraemic tourist or a resident returning from a dengue-affected area overseas.97

The CDNA case definition for dengue was changed in 2013 to accept dengue non-structural protein 1 (NS1) antigen in blood as laboratory definitive evidence for infection and a number of states and territories had been sending notifications based on a positive NS1 antigen prior to this change.

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Epidemiological situation in 2013

There were 1,841 notifications of dengue in 2013, which was 1.7 times the 5-year mean of 1,110.4 notifications. Most infections were acquired overseas (n=1,591) (Figure 78). There were 235 infections acquired in Australia. For 15 cases, no information was supplied on the place of acquisition.

Figure 78: Notified cases of dengue virus infection, Australia, 2008 to 2013, by year and month and place of acquisition

bar chart. A link to a text description follows.

Text version of Figure 78 (TXT 1 KB)

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Geographic description

More than 99% (1,826/1,841) of notifications in 2013 contained complete information on the place of acquisition. Overseas acquired infections comprised 86% of notifications (1,591/1,841) (Table 17). The number of overseas-acquired infections was the largest number ever reported, up from 1,473 in 2012, which was previously the largest number ever reported.76 Between 2007 and 2010, the number of DENV cases known to have been acquired overseas increased each year, from 254 in 2007 to 1,137 in 2010 (Figure 78).

Table 17: Notified cases of dengue virus infection, 2013, by serotype and place of acquisition
Country of acquisition Serotype Untyped Total
DENV 1 DENV 2 DENV 3 DENV 4
nfd Not further defined.
Locally-acquired
Australia
175
4
11
0
45
235
Unknown
Not stated
1
0
1
0
13
15
Overseas-acquired
Indonesia
72
36
28
7
657
800
Thailand
35
12
14
1
206
268
Philippines
9
5
1
4
44
63
India
3
5
2
0
48
58
Malaysia
3
4
0
3
43
53
East Timor
10
0
9
0
29
48
Papua New Guinea
5
6
2
0
22
35
Cambodia
4
0
4
1
22
31
South-East Asia, nfd
2
1
1
0
24
28
Sri Lanka
6
0
0
0
22
28
Vietnam
1
1
1
3
20
26
Singapore
3
3
1
1
10
18
Bangladesh
0
1
0
0
15
16
Solomon Islands
0
0
6
0
9
15
Fiji
3
2
1
0
8
14
Burma (Myanmar)
3
0
0
0
8
11
Other countries
12
3
2
4
55
76
Overseas – country unknown
1
0
0
0
2
3
Total for overseas acquired
172
79
72
24
1,244
1,591
Total
348
83
84
24
1,302
1,841

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Cases acquired in Indonesia continue to account for the largest number and proportion of all notifications, accounting for 50% (800/1,591) of all overseas-acquired cases in 2013 (Table 18), up from an average of 30% per year in 2008 and 2009, but down from an average of 60% between 2010 and 2012. DENV acquired in Indonesia was frequently serotype 1, comprising 50% of cases with a known serotype (72/143 cases), although data completeness for serotype was very low. Other frequently reported source countries in 2013 included Thailand, the Philippines, India and Malaysia.

Table 18: Notifications of dengue virus infection acquired overseas between 2008 and 2013, by selected countries of acquisition
Country of acquisition 2008 2009 2010 2011 2012 2013 Total
Indonesia
101
169
715
458
803
800
3,046
Thailand
55
24
124
85
278
268
834
India
8
15
43
29
60
58
213
The Philippines
7
9
42
23
54
63
198
East Timor
11
24
37
12
52
48
184
Malaysia
9
15
17
20
20
53
134
Vietnam
8
18
34
14
21
26
121
Papua New Guinea
13
11
21
15
16
35
111
Cambodia
5
11
5
30
31
82
Fiji
13
8
1
6
32
14
74
Sri Lanka
3
4
12
26
28
73
Total
420
472
1,137
721
1,473
1,591
5,814

All but 13 of the 235 locally-acquired cases in 2013 were reported in NNDSS to have been associated with one of the 10 outbreaks of locally-acquired infection in Queensland in 2013.98 The largest of these outbreaks was in Cairns and began in late 2012, with 141 associated notifications in 2013, the last case of them with onset in July 2013. One case in the Pilbara Region of Western Australia was locally acquired from an unknown source,99 and another case in Western Australia, while notified as locally acquired in the data on which this report is based, should have been listed as overseas acquired.

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Age and sex distribution

DENV infections acquired overseas in 2013 were most commonly reported among younger and middle aged adults (median 39 years, range 1–86 years), with a slight peak of notifications among females aged 25–29 years and males aged 50–54 years, but with similar numbers notified in all age groups between 20 and 54 years (Figure 79). Females comprised 50% (793/1,541) of overseas acquired cases.

Figure 79: Notified cases of overseas-acquired dengue virus infection, Australia, 2013, by age group and sex (n=1,591)

bar chart. A link to a text description follow

Text version of Figure 79 (TXT 1 KB)

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Locally-acquired cases peaked in several adult age groups, but was less common among people aged less than 20 years or more than 74 years (Figure 80). The median age of locally-acquired cases was 41 years (range 1 to 86 years). Females comprised 49% (116/235) of locally-acquired cases.

Figure 80: Notified cases of dengue virus infection acquired in Australia, 2013, by age group and sex (n=235)

bar chart. A link to a text description follows.

Text version of Figure 80 (TXT 1 KB)

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Seasonality

No particular pattern of seasonality was evident for overseas acquired cases of dengue, although the largest numbers were reported in July. For locally-acquired cases, only 15 cases were reported between July and October demonstrating that outbreaks are not continuing through the cooler months.

Microbiological trends

In 2013, serotype information was available for 29% of notifications (539/1,841), which was a decrease compared with the 5-year mean of 43% (Table 19). In 2013, 65% (348/539) of cases with a known serotype were due to DENV 1 in contrast to 2012, when DENV2 was more frequently reported, noting the low completeness of reporting serotype information (Table 19).

Table 19: Serotype of dengue virus infection, Australia, 2008 to 2013
Serotype 2008 2009 2010 2011 2012 2013
DENV1
40
82
190
139
81
348
DENV 1 and DENV 4
0
0
0
0
1
0
DENV 2
32
54
255
153
137
83
DENV 3
143
771
106
78
57
84
DENV 4
37
43
47
43
8
24
Untyped/unknown
309
452
630
408
1,256
1,302
Total
561
1,402
1,228
821
1,540
1,841
% with a serotype supplied
45
68
49
50
18
29

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Discussion

The number of overseas-acquired cases reported in Australia continues to increase each year. In recent years, improved diagnostic techniques, in particular the availability of the rapid NS1 antigen detection kit, have improved detection and would have contributed to the observed increase in reported numbers of overseas-acquired dengue in Australia,100 along with the dramatic re-emergence and geographical expansion of dengue overseas over the past 50 years, combined with explosive outbreaks.95

While local outbreaks of dengue occur each year in North Queensland, each outbreak is relatively small, and prompt and effective responses by public health authorities in Queensland have ensured that the disease does not become endemic there.

The number of dengue infections that are serotyped continues to decline. The decreased reporting of a serotype may reflect the increasing use of NS1 antigen detection and/or other diagnostic methods that do not provide a serotype.

Japanese encephalitis virus infection
  • Four cases of JEV were notified in 2013.
Epidemiological situation in 2013

There were 4 notifications of JEV infection in 2013. One of these notifications (a notification from Western Australia) was subsequently found not to meet the case definition. The 3 remaining cases were acquired in Thailand, Taiwan and the Philippines. There was 1 notification in 2012, and 1 notification in 2008, both acquired overseas. The last locally-acquired case was in 1998.101

Kunjin virus infection
  • Three cases of KUNV were notified in 2013.
Epidemiological situation in 2013

There were 3 notifications of KUNV infection in 2013, one each acquired in East Timor, Indonesia and Papua New Guinea. There were no notifications of KUNV infection in 2012.

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Murray Valley encephalitis infection
  • One case of MVEV was notified in 2013.
  • MVEV is a rare disease in Australia, but also acquired in the region.
Epidemiological situation in 2013

There was 1 notification of MVEV infection in 2013, acquired in Indonesia.

There was 1 case in 2012, 16 cases in 2011, 2 cases in 2008 and 4 cases in 2009. The cases notified in 2011, including an outbreak in south east Australia, have been described elsewhere.89,102–104

Malaria
  • Notifications continued the gradual decline observed since 2005.
  • One case was known to have been acquired in Australia in 2013.

Malaria is caused by a protozoan parasite in the genus Plasmodium, and 5 species are known to infect humans; Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium knowlesi.21,105 Malaria is a serious acute febrile illness that is transmitted from person to person via the bite of an infected mosquito of the genus AnopheleS. Australia was declared free of malaria in 1981,106 but suitable vectors are present in northern Australia, and the area remains malaria-receptive. Malaria is the most frequently reported cause of fever in returned travellers worldwide.107 A case series in the Northern Territory showed that malaria cases were reported in travellers returning from endemic areas, but also reflected current events such as military operations and increased refugee arrivals from malaria endemic areas.108 Malaria cases in Australia can be found either through testing of symptomatic persons with a compatible travel history, or through screening of refugees who may be asymptomatic.

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Epidemiological situation in 2013

There were 414 cases of malaria notified in Australia in 2013, a 6% decrease compared with a 5-year mean of 440 cases, and continuing the trend of gradually decreasing notifications since 2005 (Figure 81). The largest number of cases was reported by Queensland (108 cases).

Figure 81: Notified cases of malaria, Australia, 2008 to 2013, by month and year and place of acquisition

bar chart. A link to a text description follows.

Text version of Figure 81 (TXT 1 KB)

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Geographic description

Malaria in Australia is a disease associated with overseas travel or residence in areas with endemic transmission. The last cases acquired on mainland Australia were during an outbreak in North Queensland in 2002.109 Limited transmission occurs occasionally in the Torres Strait.

The place of acquisition for malaria notifications in 2013 was listed as overseas for 398 cases. For 16 cases, no place of acquisition information was supplied to NNDSS. One case in 2013 was listed as locally-acquired on Saibai Island in the Torres Strait. Prior to this case, the last known locally-acquired infections were during the 2011 outbreak in the Torres Strait.110

Complete information on the country or region of acquisition was supplied for all but eight of the cases known to have been acquired overseas, and these remaining cases were notified as being overseas acquired, country unknown or not stated. The most frequent countries of acquisition were Papua New Guinea (16% of cases with complete information) and India (16%) (Table 20). Most cases acquired in Papua New Guinea were reported by Queensland (31 cases).

Table 20: Notified cases of malaria, Australia 2013, by infecting species and region and country of acquisition
Region and country P. falciparum P. malariae P. ovale P. vivax Mixed species infection Plasmodium species Total
NFD Not further defined.
Oceania
Australia
0
0
0
1
0
0
1
Papua New Guinea
23
1
0
35
0
1
60
Solomon Islands
0
0
0
7
0
0
7
Vanuatu
0
0
0
3
0
0
3
Fiji
1
0
0
0
0
0
1
South East Asia
South-East Asia, NFD
0
0
0
1
0
0
1
Mainland South-East Asia, NFD
0
0
0
1
0
0
1
Burma (Myanmar)
0
0
0
2
0
0
2
Cambodia
1
0
0
3
0
0
4
Thailand
2
0
0
0
0
0
2
Vietnam
1
0
0
1
0
0
2
Brunei Darussalam
0
1
0
0
0
0
1
Indonesia
5
1
2
9
1
0
18
Malaysia
0
0
1
0
0
1
2
East Timor
0
0
0
0
1
0
1
North East Asia
Korea, Republic of (South)
0
0
0
1
0
0
1
Southern and Central Asia
India
2
0
0
60
1
2
65
Nepal
0
0
0
1
0
0
1
Pakistan
0
0
0
6
0
0
6
Africa
Africa NFD
1
0
0
0
0
0
1
North Africa and the Middle East
North Africa, NFD
2
0
0
0
0
0
2
Sudan
47
1
4
1
1
1
55
Western Sahara
1
0
0
1
0
0
2
Sub-saharan Africa
Sub-Saharan Africa, NFD
12
1
0
0
0
0
13
Burkina Faso
1
0
0
0
0
1
2
Cameroon
1
0
0
0
0
0
1
Congo, Democratic Republic of
2
1
0
0
0
0
3
Cote d’Ivoire
3
0
0
0
0
0
3
Equatorial Guinea
1
0
2
0
0
0
3
Gabon
1
0
0
0
0
1
2
Ghana
14
0
0
0
0
0
14
Guinea
1
0
0
0
0
0
1
Liberia
5
0
1
0
0
0
6
Mali
4
0
1
1
0
0
6
Nigeria
9
0
3
0
0
1
13
Sierra Leone
10
0
0
0
0
1
11
Togo
1
0
0
0
0
0
1
Southern and East Africa
Southern and East Africa, NFD
1
0
1
0
0
0
2
Burundi
3
0
0
0
0
0
3
Ethiopia
1
0
0
2
0
0
3
Kenya
15
1
1
0
1
0
18
Malawi
0
0
0
0
1
0
1
Mozambique
2
0
1
0
0
0
3
South Africa
2
0
0
0
0
0
2
Tanzania
10
1
1
0
0
0
12
Uganda
20
0
0
1
2
0
23
Zambia
3
0
0
0
0
0
3
Zimbabwe
1
0
0
0
0
0
1
Europe
South Eastern Europe NFD
0
1
0
0
0
0
1
Americas
Peru
0
0
0
1
0
0
1
Overseas acquired – country and region not stated/unknown
Unknown country
5
0
1
0
0
1
7
Overseas-acquired total
214
9
19
138
8
10
398
Place of acquisition unknown
7
1
0
6
2
0
16
Total
221
10
19
144
10
10
414

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Age and sex distribution

In 2013, sex was stated for all cases while age was supplied for all but 1 case. Malaria was most commonly reported in males (70%, 290/414 cases) with a peak of notifications in males aged 25 to 29 years (Figure 82). The median age of cases was 30 years (range 0–83 years).

Figure 82: Notified cases of malaria, Australia, 2013, by age group and sex (n=413)*

bar chart. A link to a text description follows.

* Age was not reported for 1 case.

Text version of Figure 82 (TXT 1 KB)

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Seasonality

Increases in notifications or an observable pattern of seasonality in a predominantly overseas-acquired infection can relate to the seasonality of travel patterns, or to local disease epidemiology in the source countries. In 2013, there was apparent increase in notifications in January and February compared with other months (54 and 55 notifications respectively, compared with an average of 30.5 notifications for the other months).

Microbiological trends

The infecting species was supplied for 98% (404/414) of cases in 2012 (Table 20). The most frequent infecting species was P. falciparum (reported in 55% of cases with complete information). P. vivax was associated with Asia and the Pacific, whilst most cases acquired in African countries were P. falciparum. In cases acquired in Indonesia and Papua New Guinea however, P. falciparum and P. vivax infections were reported in similar numbers.

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