Vaccine Preventable Diseases and Vaccination Coverage in Australia, 2003 to 2005

Rotavirus

Disclaimer: This is the fourth report on vaccine preventable disease and vaccination coverage in Australia, and is produced by the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases and the Australian Institute of Health and Welfare on behalf of the Australian Government Department of Health and Ageing published as a supplement to the Communicable Diseases Intelligence journal Volume 31, June 2007.

Page last updated: 20 July 2007

Rotavirus is a non-enveloped virus that is the major cause of acute gastroenteritis in young children and infants. Virtually all children worldwide are infected with rotavirus by 3–5 years of age. However, rotavirus occurs in all age groups.219 Rotaviruses are primarily spread by faecal-oral transmission. Infection can be asymptomatic, cause mild to moderate gastroenteritis, or severe gastroenteritis with dehydration requiring hospitalisation.219 Infection with rotavirus often confers some protection against subsequent disease.220 Severe disease occurs most commonly in those aged 6 months to 2 years.221,222 Rotaviruses are typed based on two surface proteins, VP7 (G protein) and VP4 (P protein). Viruses that contain either G1, 2, 3, 4 or 9 (and either P1a or P1b) are the five most common virus types currently circulating in Australia.223

Two vaccines became available in Australia in 2006 for the prevention of rotavirus gastroenteritis. They are to be funded under the National Immunisation Program (NIP) for all infants born from 1 May 2007. The Northern Territory has made one of the rotavirus vaccines available free of charge since 1 October 2006 for infants born after 1 August 2006. Both products are oral live attenuated vaccines for use in infants in either a two-dose course at 2 and 4 months of age (Rotarix®, GlaxoSmithKline), or a three-dose course at 2, 4, and 6 months of age (RotaTeq®, CSL Limited/Merck and Co Inc). Overall, vaccination is likely to prevent around 70% of rotavirus gastroenteritis of any severity and between 85%–100% of cases of severe gastroenteritis in immunised infants/children.224,225

Case definitions

Notifications

Rotavirus is not a nationally notifiable disease. Rotavirus became notifiable in the Northern Territory in 1994. Rotavirus became laboratory notifiable in Queensland in December 2005. Other states and territories are currently adopting passive surveillance for rotavirus infections.

Hospitalisations and deaths

The ICD-9 code 008.61(for historical data) and ICD-10 code A08.0 (rotaviral enteritis) were used to identify hospitalisations and deaths. Historical death data were reviewed from 1990–2005.

Northern Territory notification data

Northern Territory notification data for the period January 2003 to December 2005 were included in this report. Rotavirus has been notifiable in the Northern Territory since 1994. Historical notification data is published elsewhere.226 Cases notified in the Northern Territory meet the following case definition: ‘Detection of human rotavirus in stool, unless typing reveals it is rotavirus from a vaccine’.

Secular trends

In the three year review period (2002/2003 to 2004/2005), there were 10,733 hospitalisations for rotavirus (average annual rate of 18.0 per 100,000 total population). Rotavirus was recorded as the principal diagnosis in 89% of these hospitalisations (Table 18). There were more hospitalisations recorded in the first year of the review period than in the subsequent two years (2002/2003 n=4,071, 2003/2004 n=3,803, 2004/2005 n=2,859). In the previous three year period (1999/2000–2001/2002), the number of hospitalisations for rotavirus gastroenteritis was greatest in 1999/2000 before declining (Figure 39), consistent with known fluctuations in rotavirus disease activity between years.227 Rotavirus hospitalisations in temperate regions in Australia have a consistent seasonal pattern, with higher rates in the cooler months of the year from June to November. Data in the period reviewed here was consistent with this observation, with a low of 30 hospitalisations in February 2003 and a peak of 961 hospitalisations in August 2002 (Figure 37).

Figure 37. Rotavirus hospitalisations, Australia, 1993 to 2005,* by month of admission

Figure 37. Rotavirus  hospitalisations, Australia,  1993 to 2005, by month of admission

* Hospitalisations where the month of admission was between 1 July 1993 and 30 June 2005.

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Severe morbidity and mortality

The number of bed days and median length of stay (LOS) were calculated only for those hospitalisations with a principal diagnosis of rotavirus. There were a total of 23,454 bed days recorded for rotavirus (average 7,818 per year). The median LOS was two days.

The National Mortality Database ‘cause of death’ mortality records indicate a total of 14 deaths due to rotavirus over the last 15 years (1990–2004). Seven of the deaths occurred in children under five years of age, three in those aged 5–69 years, and four in adults aged over 70 years. Since 2001, only one death has been recorded.

Table 18. Rotavirus hospitalisations and deaths, Australia, 2002 to 2005,* by age group

Age group
(years)
Hospitalisations
3 years
(July 2002–June 2005)
LOS per
admission
(days)
Deaths
2 years
(Jan 2003–Dec 2004)
n (‡) Rate§ (‡) Median n Rate§
0–4
9,662
(8,601)
254.5
(226.5)
2.0
0
0
5–14
841
(779)
10.3
(9.6)
2.0
0
0
15–24
26
(18)
0.3
(0.2)
2.0
0
0
25–59
64
(50)
0.2
(0.2)
3.0
0
0
60+
140
(86)
1.4
(0.8)
3.0
1
0.01
All ages
10,733
(9,534)
18.0
(16.0)
2.0
1
0.003

* Hospitalisations where the month of separation was between 1 July 2002 and 30 June 2005; deaths where the death was recorded in 2003 or 2004.

† LOS = length of stay in hospital.

‡ Principal diagnosis (hospitalisations).

§ Average annual age-specific rate per 100,000 population.

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Age and sex distribution

Across all age groups slightly more males were hospitalised with rotavirus (male:female ratio 1.18:1). The vast majority of rotavirus hospitalisations occur in those under five years of age (n=9,662, Table 18). The age distribution of hospitalisations in children under 5 years of age can be seen in Figure 38. The highest rates of admission occurred in those aged 6–23 months (Table 19).

Figure 38. Rotavirus hospitalisation rates, Australia, 2002 to 2005,* by age group (under 5 years)

Figure 38. Rotavirus  hospitalisation rates, Australia,  2002 to 2005, by age group (under 5 years)

* Hospitalisations where rotavirus was recorded as either a principal or any other diagnosis and the month of separation was between 1 July 2002 and 30 June 2005.

Figure 39. Rotavirus hospitalisation rates, Australia, 1998 to 2005,* by age group (under 5 years) and year of separation

Figure 39. Rotavirus  hospitalisation rates, Australia,  1998 to 2005, by age group (under 5 years) and year of separation

* Hospitalisations where rotavirus was recorded as either a principal or any other diagnosis and the month of separation was between 1 July 1998 and 30 June 2005.

Table 19. R (under 5 years)

Age group
(months)
Hospitalisations
3 years
(July 2002–June 2005)
LOS per
admission
(days)
Deaths
2 years
(Jan 2003–Dec 2004)
n (‡) Rate§ (‡) Median n Rate§
0–5
1,090
(768)
320.1
(206.6)
2.0
0
0
7–11
1,773
(1,526)
476.9
(410.5)
2.0
0
0
12–23
3,519
(2,951)
470.7
(394.7)
2.0
0
0
24–35
1,849
(1,609)
243.6
(212.0)
2.0
0
0
36–47
906
(801)
117.5
(103.9)
2.0
0
0
48–59
517
(452)
66.7
(58.3)
2.0
0
0
All ages
9,654
(8,107)
256.9
(213.9)
2.0
0
0

* Hospitalisations where the month of separation was between 1 July 2002 and 30 June 2005; deaths where the death was recorded in 2003 or 2004.

† LOS = length of stay in hospital.

‡ Principal diagnosis (hospitalisations).

§ Average annual age-specific rate per 100,000 population.

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Geographical distribution

Over the period 2002/2003 to 2004/2005, the Northern Territory recorded over five times the Australian average rate of hospitalisation for rotavirus gastroenteritis (Northern Territory rate: 99.3 per 100,000 population) (Appendix 3). Victoria had the lowest rate of hospitalisation (8.5 per 100,000 population), less than half the Australian average. However, comparison of hospitalisation rates between jurisdictions is complicated by likely differences in testing practices for rotavirus, which may, in part, explain the differences in observed rates of hospitalisation.221,228

Northern Territory notification data, rotavirus

A total of 901 cases were notified from January 2003 to December 2005, an average annual rate of 149.7 per 100,000 total population. In 2004, there were almost twice as many notifications (n=407) as in 2002 (n=238) or 2005 (n=256). The male to female ratio amongst notified cases was 1.26:1.

The rate of notification for rotavirus was significantly higher than the hospitalisation rate in the Northern Territory. The notification data from the Northern Territory generally has a younger age structure than hospitalisation data from all of Australia (Figure 40).

Figure 40. Rotavirus notifications, the Northern Territory, 2003 to 2005,* by age group (under 5 years)

Figure 40. Rotavirus  notifications, the Northern Territory,  2003 to 2005, by age group

* Notifications that were recorded between 1 January 2003 and 31 Dec 2005.

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Comment

Rotavirus is responsible for a significant number of hospitalisations in Australia each year (around 3,500 hospitalisations were recorded annually with either a principal or non-principal diagnosis of rotavirus). The primary disease burden is in those under five years of age, with hospitalisations most common in the first two years of life. Universal immunisation of infants in the first six months of life under the NIP should prevent the majority of severe cases of rotavirus and it is anticipated that hospitalisation rates will be substantially reduced. However, it will be important to encourage timeliness of vaccination in order to ensure a maximal impact upon disease. Ongoing analysis of national hospitalisation data will provide valuable data to help assess the impact of a national vaccination program.

In addition to the caveats required in the interpretation of hospitalisation data, the use of the specific rotavirus code (A08.0) for quantifying rotavirus hospitalisations has substantial limitations. Although hospitalised patients with laboratory-confirmed rotavirus infection are likely coded as rotavirus gastroenteritis, laboratory testing for rotavirus antigen in stool specimens of children hospitalised with acute gastroenteritis is not often conducted. Clinical guidelines for the management of acute uncomplicated gastroenteritis do not recommend routine stool testing for confirmation of the aetiological agent.229 Several international studies have shown that measurement of rotavirus hospitalisation rates utilising the specific rotavirus code underestimated the true number of rotavirus-associated hospitalisations.230,231 Two Australian studies have estimated the burden of rotavirus hospitalisations, as a percentage of the number of acute gastroenteritis (AGE) hospitalisations using distinct methodologies. Both studies, conducted a decade apart, estimated that rotavirus is responsible for approximately 10,000 hospitalisations annually.228,232 In addition, emergency department visits for rotavirus were estimated as a percentage of AGE emergency department visits at approximately 21,500 annually.232 These estimations may be a more accurate picture of the true hospitalisation disease burden.

The Australian Rotavirus Surveillance Program was initiated in June 1999 to monitor changes in the distribution of rotavirus serotypes over time. Historically, the dominant serotype in Australia and worldwide has been G1.233 Recent surveillance reports noted a dramatic increase in the prominence of the G9 serotype in the years 2002–2003,234,235 followed by a decline in G9 prevalence in subsequent years.223,236 It appears likely that both rotavirus vaccines are effective against the G9 serotype, as well as the majority of other serotypes detected in Australia.224,225

Data from the Northern Territory hospitalisations and notifications emphasises the higher burden of disease in the region, particularly in Indigenous infants and children. Historically, the Northern Territory has experienced epidemics of rotavirus on the background of endemic disease.226 These epidemics are thought to result from the relative isolation of remote communities with a lack of circulating strains, which then see a rapid spread of infection upon reintroduction of the virus.226,237,238

Compared with other developed countries, Australia has a relatively high rate of hospitalisation, with an estimated one in 26 children hospitalised by five years of age.232 In Europe it is estimated that one in 50 children are hospitalised by the age of five years, although estimates vary by country and study methods.239 Although there are limited data on nosocomial rotavirus infections in Australia, it is recognised as a significant problem in paediatric wards and hospitals, with at least 14%–19% of all rotavirus infections being hospital acquired.240,241 Timely vaccination should control this.

Acknowledgements: Rosalie Schultz, Peter Markey and Christine Selvey, Centre for Disease Control, Northern Territory.

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