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Results - Part B: Analysis of data by pathogen

Measles, mumps and rubella viruses

LabVISE reports of measles, mumps and rubella during the study period have declined since 1994, when the last epidemic of measles occurred in Australia. As part of Australia's measles elimination strategy, the Measles Control Campaign in 1998 vaccinated 1.7 million Australian children regardless of their vaccination status, with the measles-mumps-rubella vaccine (MMR). As a result of this campaign and continuing high vaccination coverage, measles activity in Australia is at an historic low.⁷

Measles, mumps and rubella are notifiable diseases that have been collected since 1991 from all Australian states and territories in the National Notifiable Diseases Surveillance System. A comparison of notifications for these diseases recorded in the NNDSS with LabVISE laboratory reports is shown in Table 12.

Table 12. Laboratory reports to LabVISE and notifications to NNDSS of measles, mumps and rubella, 1991 to 2000

Virus	Surveillance system	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Measles	LabVISE	256	204	853	1,199	153	57	67	49	172	44
	NNDSS	1,380	1,425	4,536	4,825	1,194	481	858	290	230	107
Mumps	LabVISE	32	48	77	87	69	37	40	44	58	49
	NNDSS	NN	23	28	90	157	126	191	182	184	212
Rubella	LabVISE	246	753	926	1,178	735	716	362	103	145	51
	NNDSS	620	3,810	3,812	3,374	4,590	2,556	1,389	745	376	321

NN Not notifiable

Measles reports in LabVISE included both viral isolations and seroconversions, whereas the NNDSS included cases of measles diagnosed on the basis of clinical findings or epidemiological links to another case. NNDSS notifications were 4-8 times higher than LabVISE reports. Laboratory confirmation of measles infection becomes increasingly important as Australia plans the elimination of the disease over the next few years. LabVISE laboratories could provide important information to supplement that of the NNDSS if a representative sample of all diagnostic laboratories was included. Despite these limitations, laboratories can provide important information on circulating measles virus genotypes in Australia. Genotyping data suggests that in some jurisdictions there are now no endemic measles strains circulating and that small outbreaks are frequently linked to imported cases (Lambert, Communicable Disease Conference 2001, abstract 60).

Surveillance of mumps in LabVISE preceded that in the NNDSS. Mumps notifications to the NNDSS began in 1992 and for some years, mumps was not reported from all jurisdictions. Thus from 1991 to 1993, LabVISE recorded more cases of mumps than the NNDSS. Notifications to the NNDSS include clinically diagnosed cases without laboratory confirmation, although some jurisdictions such as New South Wales require laboratory confirmation. Mumps is a rare disease in Australia. Although vaccination of Australian children with the MMR vaccine is expected to reduce mumps incidence in Australia, the impact has been less evident on the rate of mumps compared with the rate of measles (Gidding, Communicable Disease Conference, 2001, abstract 57). In a similar manner to measles, the laboratory diagnosis of mumps increases in importance, as the disease becomes rarer.

The incidence of rubella in Australia has been dramatically reduced as a result of widespread vaccination with MMR. Both NNDSS and LabVISE data show the impact of increased vaccination in Australia during the 1990s. Up to 2000, notifications of rubella to the NNDSS were clinically defined and did not require laboratory confirmation.

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Hepatitis viruses

Up to 1996, hepatitis B and C were the predominant reports of hepatitis in LabVISE (Table 5). These reports were excluded from LabVISE from 1997 and were not analysed in this report. Hepatitis A and D were reported for the whole study period and hepatitis E has been reported since 1992. LabVISE reporting of hepatitis D and E pre-dated reporting through the NNDSS by some years (Table 13) and reports from all states and territories to the NNDSS was not achieved for hepatitis D and hepatitis E until 2000.

Table 13. Laboratory reports to LabVISE and notifications to NNDSS of hepatitis A, D and E, 1991 to 2000

Virus	Surveillance system	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Hepatitis A virus	LabVISE	445	371	451	363	424	407	624	384	375	146
	NNDSS	2,195	2,109	2,006	1,919	1,645	2,112	3,069	2,443	1,557	807
Hepatitis D virus	LabVISE	37	45	47	24	23	17	15	7	8	9
	NNDSS	NN	NN	NN	5	37	14	17	10	21	27
Hepatitis E virus	LabVISE	-	1	12	6	8	2	4	1	1	4
	NNDSS	NN	NN	NN	1	5	4	7	1	2	10

NN Not notifiable.

Since the peak of notifications to NNDSS in 1997, the number of cases of hepatitis A has fallen significantly as a result of vaccination of high-risk groups. The trends in the NNDSS data have been reflected in the trends in LabVISE data. Hepatitis notifications to NNDSS include clinical cases of hepatitis and cases epidemiologically linked to a serologically confirmed case, and thus are expected to outnumber the laboratory-confirmed cases reported by LabVISE.

Since hepatitis D is diagnosed only by laboratory methods, LabVISE data should be close to that in NNDSS, subject to the limited number of laboratories contributing to LabVISE. In some jurisdictions (New South Wales and the Northern Territory), cases of hepatitis E (HEV) may be clinically defined as a hepatitis-like illness in the absence of other causes of hepatitis with a history of travel to HEV-endemic areas.

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Arboviruses

The numbers of arthropod-borne ('arboviruses') diseases reported in LabVISE between 1991 and 2000 are shown in Table 14.

Table 14. Laboratory reports to LabVISE of arboviruses, 1991 to 2000

Virus	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	Total
Ross River virus	833	1,319	1,895	2,240	988	3,249	2,016	676	1,423	1,268	15,907
Barmah Forest virus	36	251	208	273	202	232	201	44	180	169	1,796
Dengue total	29	385	528	35	25	62	64	70	88	181	1,467
Flavivirus (unspecified)	29	47	104	23	45	21	21	73	27	40	430
Kunjin virus	14	10	-	2	5	5	6	5	5	4	57
Murray Valley encephalitis virus	10	1	9	3	-	-	3	2	2	20	50
Japanese encephalitis virus	-	-	-	1	6	-	-	1	1	-	9
Stratford virus	3	-	-	-	-	1	-	1	-	-	5
Kokobera virus	1	-	-	-	-	-	-	-	-	-	1

Of the 8 arboviruses that were reported to LabVISE, three (Ross River virus, Barmah Forest virus and dengue) were also notifiable diseases reported to the NNDSS during the same period. Another 3 viruses (Murray Valley encephalitis virus, Kunjin virus and Japanese encephalitis virus) had been notifiable to NNDSS under the collective group Australian encephalitis but from 2001 became notifiable separately. The NNDSS also recorded 'Arbovirus unspecified' as a disease category in the period 1991 to 2000, which would have captured data on all other viruses listed here.

A month by month comparison of notifications of Ross River virus (RRV) to NNDSS and laboratory reports of RRV to LabVISE is shown in Figure 4. LabVISE reports show a seasonal variation matching that seen in the NNDSS notifications, with annual peaks in the first and second quarters (i.e. the summer months) of the year. RRV infection is diagnosed by virological or serological methods. The smaller numbers reported to LabVISE in the same time period, reflects the small number of laboratories contributing to LabVISE. The number of LabVISE reports were similar to the number of NNDSS notifications out of epidemic seasons (Figure 4).

Figure 4. Laboratory reports to LabVISE and notifications to NNDSS of Ross River virus infection, 1991 to 2000, by month of specimen collection



Barmah Forest virus laboratory reports have been recorded in LabVISE since 1991, 4 years before notifications were included in the NNDSS. A comparison of LabVISE reports and NNDSSnotifications by month between 1991 and 2000 is shown in Figure 5. As for RRV, LabVISE laboratory reports and NNDSS notifications show an annual peak in the summer months. LabVISE reports were a larger proportion of NNDSS notifications out of epidemic seasons (Figure 5).

Top of pageFigure 5. Laboratory reports to LabVISE and notifications to NNDSS of Barmah Forest virus infection, 1991 to 2000, by month of specimen collection



LabVISE reports of dengue virus include some data on the serotypes of dengue virus isolated (Table 5). However, the proportion of dengue virus among each year's reports that were serotyped has declined, particularly in recent years (Table 5) and there is no way to tell from LabVISE data whether the dengue infection was acquired overseas. The movement of new serotypes of dengue virus into Australia has important implications. The frequency of dengue haemorrhagic fever, a serious complication of dengue virus infection, increases when previously infected populations are exposed to different serotypes of the dengue virus. Since dengue is a major public health problem in areas to the north of Australia, and is occasionally a significant problem in Far North Queensland, surveillance of dengue and circulating dengue viral serotypes is essential.

Table 15. Laboratory reports to LabVISE of dengue virus, 1991 to 2000, by virus serotype

Virus	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Dengue type 1	13	9	1	-	3	-	-	-	-	-
Dengue type 2	3	297	422	4	1	29	20	-	-	2
Dengue type 3	-	5	2	4	2	2	1	27	3	4
Dengue type 4	1	-	-	1	-	1	-	-	-	-
Dengue not typed	12	74	103	26	19	30	43	43	85	175
Dengue total	29	385	528	35	25	62	64	70	88	181

LabVISE reports of Murray Valley encephalitis virus infections are an important but partial record of this significant pathogen. Murray Valley encephalitis became a separately nationally notifiable disease from January 2001 along with Kunjin. Other arboviruses are also reported to the NNDSS as Arbovirus (not elsewhere classified).


This article was published in Communicable Diseases Intelligence Volume 26, No 3, September 2002