Prevalence of chronic hepatitis B in South Western Sydney: evaluation of the country of birth method using maternal seroprevalence data
Ms Caroline Turnour, Centre for Aboriginal Health, NSW Department of Health, Locked Mail Bag 961, North Sydney, NSW 2059; e-mail: email@example.com
Objective: To estimate the prevalence of hepatitis B infection and evaluate the country of birth (Census) method of describing hepatitis B distribution in an Australian health service with a large migrant population.
Methods: The prevalence of chronic hepatitis B in Sydney South West Area Health Service (SSWAHS, population 1.3 million) was estimated by applying the prevalence of hepatitis B surface antigen (HBsAg) in high or intermediate hepatitis B prevalence countries to SSWAHS residents from those countries, using 2006 Census data. The Australian hepatitis B prevalence (0.7%) was applied to the remainder. This method was validated using HBsAg seroprevalence in 42,274 women aged 15–44 years who delivered at SSWAHS public maternity hospitals during 2007 to 2009.
Results: The SSWAHS prevalence of HBsAg using the Census method was 2.0% for all ages and 2.3% for 15–44 year old women. The seroprevalence in 15–44 year old mothers was 1.8%. The adjusted population prevalence was 1.6%. The two methods produced broadly similar descriptions of relative hepatitis B burden by local government area and country of birth.
Conclusion: The Census method overestimates the prevalence of hepatitis B infection by 30%, but produces similar patterns of hepatitis B burden across the area. Health services can estimate the prevalence and distribution of chronic hepatitis B using readily available data to focus delivery of prevention and treatment services.
Chronic hepatitis B infection contributes substantially to the global burden of cirrhosis and hepatocellular carcinoma. Approximately 30% of people who acquire the virus perinatally and 5–10% who acquire it as adults are at risk of liver disease.1 Hepatitis B is preventable and increasingly treatable: immunisation at birth prevents transmission and access to treatment may delay or reverse the progression of liver cancer and cirrhosis.2 Studies suggest the greatest need for hepatitis B services is in countries with high (>8%) or intermediate (2–8%) prevalence of hepatitis B, or areas with large migrant populations from these countries.3–8
Australia is classified as a low prevalence (<2%) country with national laboratory- based serosurveys estimating the hepatitis B prevalence to be between 0.5 and 0.7%.7,9 Sydney South West Area Health Service (SSWAHS) is a large and diverse health service with a population of 1.3 million in Sydney, New South Wales (NSW), Australia. Overseas-born people make up 36% of the Area's population including 24% born in countries with intermediate or high hepatitis B prevalence. The local population prevalence of hepatitis B in SSWAHS is not known, but the distribution of hepatitis B is thought to be concentrated within local government areas (LGAs) with high migrant populations. Better information about the distribution of hepatitis B within our Area is needed in order to plan services to prevent and treat hepatitis B.
In this paper we use two methods to estimate the prevalence of hepatitis B in SSWAHS. We explored the utility of the country of birth method (Census) of estimating population hepatitis B prevalence in an area with a high migrant population by comparing the results with a population-based estimate of seroprevalence in a population sub-group (SSWAHS mothers aged 15–44 years) by age group, country of birth and local government area.
This study received approval from the SSWAHS Ethics Committee (Eastern Zone).
Using two methods, we estimated the prevalence and epidemiology of chronic hepatitis B infection in SSWAHS residents.
To maximise the number of prevalence studies that could be included in the country of birth method; to allow comparison with the maternal seroprevalence method; and to reduce complexity of the model, we assumed that detection of hepatitis B surface antigen indicated chronic hepatitis B infection.
Maternal seroprevalence (hospital delivery) method
Around 74% of all SSWAHS residents who delivered in hospitals in 2006/07 were delivered in SSWAHS public hospitals. Of the remainder, around 11% delivered in public hospitals outside SSWAHS, and 15% delivered in private hospitals.10
We determined the hepatitis B status of all women who delivered in all seven public maternity hospitals in SSWAHS during 2007 to 2009 using data extracted from the electronic medical record, and compared our cohort to the state-wide reference data collection (NSW Midwives Data Collection) for 2007/08. After adjusting for hospital of delivery, we determined the SSWAHS prevalence of hepatitis B in post-partum women by country of birth, age group and LGA.
As maternal seroprevalence data was relatively under-ascertained in one SSWAHS public hospital, the records of mothers were adjusted to account for hospital of delivery by weighting the mothers’ records against the Midwives Data Collection by hospital of delivery.
Country of birth (Census) method
Prevalence of chronic hepatitis B by country of birth was classified using the World Health Organization (WHO) classification: low (<2%), intermediate (2–8%) and high prevalence (>8%) countries.11
Using the 2006 Australian census, the SSWAHS prevalence of hepatitis B was estimated by applying the country of birth prevalence of chronic hepatitis B infection to migrants from 41 high or intermediate prevalence countries/regions, with a SSWAHS population greater than 1,000 people. We reviewed the literature for the best available estimate of hepatitis B prevalence for these countries (Table 1). The WHO estimate was used for countries with poor or limited hepatitis B prevalence data.11–13 The Australian population prevalence of 0.7% was applied to all other residents.7 We calculated an estimate of the overall prevalence of chronic hepatitis B infection in SSWAHS, as well as the burden of disease by country of birth and estimates of prevalence by age group, country of birth and local government area.
Table 1. Comparison of prevalence of chronic hepatitis B using country of birth and maternal seroprevalence methods, SSWAHS high and intermediate prevalence countries and Australia, 2007–2009.
|High prevalence (>8%)|
|Viet Nam||1119||8.7 (7.7–9.7)|
|South Africa, Republic of||1021,22||0.6 (0.0–1.8)|
|Intermediate prevalence (2–8%)|
|Hong Kong||825||2.0 (0.0–4.3)|
|Former Yugoslaviab||432,33||0.7 (0.02–1.5)|
|Korea, Republic of (South)||434||2.4 (0.9–3.9)|
|Samoa, Western||418||3.1 (1.3–4.9)|
The population of SSWAHS in 2006 was 1.3 million people of whom 313,107 (24%) people were born in 41 countries classified as high or intermediate hepatitis B prevalence exclusive of those with a SSWAHS population of less than 1,000 migrants (0.07% of the total SSWAHS population).14 The remainder of the SSWAHS population were born in Australia (709,068 people; 55%), born in a low prevalence country/region or in a country/region of birth with less than 1,000 residents residing in SSWAHS (155,849 people; 12%), or their place of birth was not stated (114,167; 9%).
During 2007 to 2009, 51,927 deliveries were extracted from the seven SSWAHS public hospital electronic record system. When the deliveries registered in those hospitals are compared with the reference state-wide data collection for 2007/08 (NSW Midwives’ Data collection), 99% of deliveries had been captured electronically. Of these records, 705 (1.4%) were for multiple births, 4,158 (8%) were subsequent births in the same woman, 3,490 (7.4%) were not residents of SSWAHS, 1,206 (2.8%) were missing hepatitis B status information, and 94 records were for women aged under 15 or over 45 years. These records were excluded, leaving the records of 42,274 women aged 15–44 years available for the maternal seroprevalence analysis.
The prevalence of hepatitis B in 15–44 year old SSWAHS mothers was 1.82%, ranging from 0.4% in mothers born in Australia, to 11.7% in mothers born in Taiwan (Table 1). The countries of birth which provided the greatest burden of disease were Vietnam, China, Australia and Cambodia (Table 2). Prevalence increased with maternal age (Table 3).
Table 2. Comparison of burden of chronic hepatitis B infection in women aged 15–44 years using country of birth and maternal seroprevalence methods, by top 4 country of birth, Sydney South West Area Health Service.
Table 3. Comparison of prevalence of chronic hepatitis B by age group using country of birth (2006) and maternal seroprevalence methods (2007–2009), Sydney South West Area Health Service.
|0–4 years||0.8||0.8||0.8|| |
|5–9 years||0.9||0.9||0.9|| |
|10–14 years||1.1||1.0||1.1|| |
|15–19 years||1.5||1.5||1.5||0.8 (0.3–1.3)|
|20–24 years||2.1||2.2||2.1||1.5 (1.2–1.8)|
|25–29 years||2.2||2.4||2.3||1.9 (1.6–2.1)|
|30–34 years||2.2||2.4||2.4||1.9 (1.6–2.1)|
|35–39 years||2.4||2.6||2.5||2.0 (1.7–2.3)|
|40–44 years||2.7||2.8||2.8||2.3 (1.6–3.1)|
|45–49 years||2.8||2.8||2.9|| |
|50–54 years||2.6||2.7||2.7|| |
|55–59 years||2.3||2.3||2.3|| |
|60–64 years||2.1||2.0||2.1|| |
|65–69 years||2.0||2.1||2.1|| |
|70–74 years||2.1||2.1||2.1|| |
|75–79 years||2.0||1.9||2.0|| |
|80 and over||1.8||1.7||1.8|| |
|Total (15–44 years)||2.2||2.3||2.3||1.8 (1.7–2.0)|
The Census (country of birth) method provided a SSWAHS population prevalence of chronic hepatitis B infection of 2.0% (Table 3). Using the method, 74% of the population estimated to have chronic hepatitis B in SSWAHS were born in a high or intermediate hepatitis B country/region as classified by WHO, with 33% of SSWAHS residents with hepatitis B born in Vietnam or China. Each of the remaining 39 countries contributed less than 4% of the total hepatitis B burden. Looking at females aged 15–44 in particular; the top two countries of birth with the greatest burden of disease were again Vietnam and China (Table 2).
The prevalence in the overall SSWAHS population was higher in all age groups than the general Australian prevalence, while the prevalence was consistently above 2.0% in adults 25–59 years (Table 3). The prevalence in 15–44 year old women was 2.3%– an absolute 0.5% or relative 30% higher than the maternal seroprevalence estimate. After adjusting the estimate of population prevalence downwards in line with the maternal seroprevalence estimate, the population prevalence of hepatitis B in SSWAHS was 1.6%, representing 21,700 people in 2009. Women accounted for 52% of the population born in intermediate to high prevalence countries.
The distribution of disease prevalence by LGA using the Census method was similar to that derived from the maternal seroprevalence, but varied substantially from 0.8–3.4% by LGA (Table 4).
Table 4. Comparison of prevalence of chronic hepatitis B using country of birth and maternal seroprevalence methods, SSWAHS 2007–2009, by local government area.
|Canada Bay||65,748||1.5||0.9 (0.4–1.3)|
|Sydney, City of (SSWAHS)||82,984||1.8||1.6 (1.0–2.1)|
We found the estimated prevalence of chronic hepatitis B in a health service with a high proportion of migrants from intermediate and high prevalence countries to be 2.2 times higher than in the general Australian population. This finding is consistent with a Victorian seroprevalence survey, which found regional differences ranging from 0% to 7.2% in Melbourne with higher rates corresponding to areas with a higher proportion of overseas-born residents.3 Using an adjusted population prevalence of 1.6%, 21,700 SSWAHS residents have chronic hepatitis B in 2009. Based on 30% of chronic hepatitis B carriers from high or intermediate hepatitis B prevalence country (4,800 people) and 5% of the remaining chronic hepatitis B carriers (280 people) developing complications, we estimate that 5,080 people in SSWAHS are at risk of developing severe complications of the disease.1
Further, the burden of disease was unequally distributed across the Area, with communities with high proportions of overseas- born residents having a population prevalence comparable to an intermediate prevalence country. These communities need public health strategies that promote vaccination, early diagnosis and appropriate referral for antiviral therapy assessment as well as liver cancer and liver disease screening programs especially for high-risk migrant populations from South-East Asia, China and Africa.
Reliable methods of identifying these communities are therefore needed to assist health service planning. This need is amplified by the lack of population-based local prevalence studies and the limitations of routine laboratory notifications, which are dependent on testing and reporting patterns.15
Our study demonstrates that the census method provides high quality information about the distribution of hepatitis B within a region. Past studies have also used this method16 but the validity of the Census method as a service planning tool has not been previously evaluated. We found that the Census method overestimated the absolute prevalence by around 30%, however, the relative distribution of the burden of disease by Local Government Area followed a similar pattern to the results obtained using maternal seroprevalence data.
Poor quality or out-of-date global hepatitis B prevalence data reduces the accuracy of the Census method. The prevalence estimates applied for intermediate and high hepatitis B countries were drawn from studies that used different methods of variable quality over different periods. The poor quality of global prevalence data also prevented incorporating the impact of childhood immunisation programs into the Census method.
We assumed that the hepatitis B prevalence of migrants is similar to that of the general population in the country of birth. This may be incorrect for several reasons: migrants may come from a higher or lower socioeconomic background than average or come from a distinctive region or ethnic group. This is suggested in our results for South Africa and Egypt but less so for Vietnam and China and highlights the need to consider how well the migrant population represents the prevalence in their country of birth when using the Census method.
True seroprevalence rates by country of birth in our maternal population were consistently and in some cases substantially lower than that reported in the country of birth, suggesting a common pattern of lower seroprevalence in migrants, perhaps due to the ‘healthy migrant’ effect.17
In addition, our estimate of maternal seroprevalence was limited to mothers who delivered in public hospitals, who may differ from those who choose to deliver in private hospitals. It is possible that this led to an overestimate of maternal hepatitis B prevalence in SSWAHS.
Using the prevalence estimate of 0.7% for Australian born individuals may also inflate the country of birth results as this figure is drawn from national serosurveys, which included migrants from high and intermediate prevalence countries.
Many studies report prevalence based on one positive HBsAg surface antigen test, despite a chronic hepatitis B diagnosis requiring a second test six months later. Correcting for these limitations would introduce a complexity to the method that would compromise its local utility. This limitation means that estimates of prevalence using either method may be inflated.
There is evidence that the prevalence of hepatitis B varies by sex, with higher prevalence in males.3 This suggests that our maternal seroprevalence estimates may underestimate the true population prevalence, and that the census method may not overestimate the population prevalence as much as we have estimated.
In the census method, the Australian prevalence rate was applied to 114,167 (9%) of the SSWAHS population who did not state their place of birth. Our country of birth estimate may be lower because of this assumption but the effect is likely to be small.
A final limitation of the census method is that it is unable to provide an estimate of differences in prevalence related to an area's Aboriginal population. There are large variations across Australia in studies of the prevalence of chronic hepatitis B in Indigenous populations1 and we found no reasonable estimate to apply to the SSWAHS Aboriginal population. Other methods such as the antenatal seroprevalence method are required to estimate prevalence in these populations.
There is commonly limited or no information on the local prevalence of hepatitis B. We have demonstrated and evaluated a straightforward method of obtaining detailed epidemiological data on hepatitis B in local areas with large migrant populations from intermediate and high prevalence hepatitis B countries, using country of birth prevalence data combined with Census data. These areas may carry a hepatitis B burden comparable to that of an intermediate prevalence country. Affected communities require a public health response that draws on best available data to develop a co-ordinated response.
This study has highlighted the limitations of the country of birth method and the need to adjusts its estimates downwards where possible using a known prevalence such as maternity seroprevalence data. Nevertheless, in the absence of local seroprevalence data, the information obtained through the census method is of value in supporting local planning and will assist public health units, primary care providers, laboratories and specialist providers to work together to deliver services that prevent further transmission, promote early diagnosis and improve liver disease survival rates.