Delivering a Healthy WA
Disease WAtch

Review of Notifiable Diseases, 2011

Western Australia had 30,467 communicable disease notifications in 2011, a 21% increase on the number of notifications in 2010, and the highest number ever recorded. This increase is largely accounted for by an additional 2,563 pertussis notifications in 2011, and smaller increases in the number of chlamydia, Ross River virus and gonorrhoea notifications.

The most frequently notified diseases in 2011 were genital chlamydia (11,762 cases), pertussis (4,021), varicella-zoster infection (2,373), campylobacteriosis (2,205), influenza (1,889), gonorrhoea (1,840), and salmonellosis (1,323).

Enteric Diseases

The number of notifications for campylobacteriosis in 2011 (n=2,205) was similar to the mean of the previous 4 years (n=2,218), but the number of salmonellosis notifications (n=1,323) was 25% higher than the previous 4-year mean. The increase in salmonellosis was largely attributable to an increase in the number of cases who had acquired their infection in Bali, Indonesia.

There was a large decrease in rotavirus notifications in 2011 (n=183) when compared to the previous 4-year mean (n=552). Whilst much of the decrease may be attributed to the rotavirus vaccine program, a change in laboratory testing and notification practices for rotavirus is also likely to have contributed.

The notification rate for cryptosporidiosis in 2011 was 56% higher than the mean of the previous 4 years, due to a community-wide increase in the January to April period.

The number of shigellosis notifications in 2011 (n=86) was lower than for any of the previous 4 years, reflecting a reduction in Shigella flexneri notifications, particularly in Aboriginal people from the Pilbara and Kimberley regions.

Hepatitis A notifications were 50% lower in 2011 (n=13) than the historical 4-year mean, with lower notification numbers for both WA and overseas-acquired cases.

For all of the major enteric infections, with the exception of hepatitis A, notification rates were highest in the age group 0 to 4 years age group. For most enteric infections, notification rates were also higher for Aboriginal people than non-Aboriginal people. The greatest difference was for shigellosis, with the notification rate for Aboriginal people 28 times the rate in non-Aboriginal people. For most of the enteric diseases, the remote regions had the highest notification rates for both Aboriginal and non-Aboriginal people, with the Kimberley having the highest rates for salmonellosis, cryptosporidiosis and shigellosis.

There were 7 cases of listeriosis notified in 2011. Two cases were pregnant women, one of whom miscarried at 14 weeks gestation and the other who delivered a live baby at 30 weeks gestation. The 3 shiga-toxin producing E. coli notifications in 2011 were all males who either had contact with farm animals or had eaten foods considered to be high risk.

Typhoid and paratyphoid fever notifications were higher in 2011 than the previous 4-year mean. This was due largely to an increase in infections acquired in India (increasing from 3 cases in 2007 to 15 in 2011).

Vibrio parahaemolyticus notifications were also higher in 2011 than the previous 4-year mean, due to an increase in overseas-acquired infections. The most common countries of acquisition in 2011 were Indonesia (n=5) and Thailand (n=3). One case of cholera was notified in 2011, with infection acquired in the Philippines.

Three of 4 hepatitis E notifications in 2011 were for navy personnel who had travelled on a ship that visited Oman and India before returning to WA in November. Infection was most likely acquired during shore visits in these countries or from food brought on board during these shore visits.

Gastrointestinal disease outbreaks

There were 10 significant outbreaks of food-borne or suspected food-borne disease identified in WA in 2011. Five of these outbreaks were caused by Salmonella species, one by both Salmonella and Campylobacter, one by norovirus, and for 3 outbreaks the infectious agent or toxin was unknown. The largest food-borne outbreak in 2011, which resulted in 65 people becoming ill, was caused by a combination of Salmonella and Campylobacter infection, with illness significantly associated with eating duck parfait served at a large function. The next largest food-borne outbreak, with 53 people ill, was due to norovirus, and occurred amongst patrons and staff members at a hotel. Illness was significantly associated with eating salad.

Salmonella Typhimurium (STM) was the cause of 5 outbreaks with different pulsed field gel electrophoresis (PFGE) types. Significant STM outbreaks included one in January due to PFGE type 0001 (phage type 9) that caused illness in at least 15 people who had consumed Vietnamese pork rolls. Secondly, there were 24 people notified with STM PFGE type 0003 (phage type 135) infection who had eaten different meals at the same restaurant between January and March. Food-handling deficiencies were identified at the restaurant but the source of contamination was not found. Thirdly, there was an STM outbreak due to PFGE 0386 (phage type 193) that caused illness in 30 people who attended a private party. Several foods were associated with illness but the source of the Salmonella contamination was not identified. Finally, an STM outbreak due to phage type 135a affected 7 crew and 7 passengers on a cruise ship operating from WA that had visited Papua New Guinea. The investigation did not identify a clear association between illness and a specific food item.

There were 91 non-food-borne gastroenteritis outbreaks reported in WA in 2011, 11% fewer than in the previous year. The causative agent for 42% (n=38) of these outbreaks was confirmed as norovirus, and Cryptosporidium was the cause of 5 outbreaks. Non-food-borne outbreaks were predominantly associated with institutional settings, particularly residential care facilities (78%) and childcare centres (11%).

Vaccine-preventable diseases

A pertussis epidemic began in WA in mid-2011 (see Figure 1). The number of cases notified in 2011 (n=4,021) was more than 5 times the previous 4-year mean (n=711), and double the number notified (1,996 cases) during the previous epidemic in 2004. Notification rates were highest in the 5 to 9 year age group (529 cases per 100,000 population), followed by those aged 10 to 14 years (468/100,000), and children under one year old (360/100,000). There was also a later peak in adults aged 35-44 years (165/100,000). Pertussis notification rates were highest in the Kimberley, Great Southern and Southwest regions, while the Goldfields and Midwest regions had significantly lower notification rates than the rest of the state.

Figure 1: Number of pertussis notifications in Western Australia by  month, 2010 and 2011.

Figure 1: Number of pertussis notifications in Western Australia by month, 2010 and 2011.

There was a small increase in influenza notifications from 2010 to 2011, with activity reflecting a relatively moderate season (n=1,889). Activity peaked in August, and there was unusually high inter-seasonal activity into the January to March period. Influenza A strains were dominant in 2011, with a significant increase in influenza A/H3N2 detections compared to 2010. Overall, notifications comprised an estimated 54% A/H1N1 (2009), 33% A/H3N2 and 13% influenza B strains, and notification rates were highest in the northern part of the state. The proportion of influenza cases who were hospitalised in 2011 (33%) was higher than the mean of the previous 4 years (19%), although this may at least partly reflect better ascertainment. There were 22 deaths reported among notified influenza cases in 2011.

There has been no endemic measles transmission in WA since the late 1990s, and the number of measles notifications remains low, associated with importation from overseas and occasional limited local transmission. There were 17 measles cases in 2011, 10 of which were overseas-acquired: from Indonesia (n=3), New Zealand (n=3), Thailand (n=2), and single cases from the Philippines and Malaysia. Of the 7 “locally acquired” infections, 2 cases were infected while working on an off-shore vessel with an index case who was a fly-in worker from New Zealand; 1 case was infected by one of the former cases while in transit at Darwin airport; 2 cases acquired infection from an older sibling who was infected in Thailand; and 1 case was infected by a WA resident who acquired infection in New Zealand while attending the Rugby World Cup. One atypical measles case, for whom no source of infection could be identified, most probably had a false-positive laboratory result. The age range for cases was 0 to 46 years; 7 were unvaccinated, 1 child had received 1 vaccine dose, 1 was below vaccination age, and 8 had unknown vaccine status.

Rubella has also been eliminated as an endemic disease in WA. However, 2 clusters of locally acquired rubella in 2011 contributed to an increase in case numbers (n=15) above the previous 4-year mean (n=5). One cluster comprised a group of 6 adult workers in one office, with the source assumed to be an unidentified person who had acquired infection overseas. In the second cluster, a female acquired her infection in WA, also from an unknown source, and transmission occurred to her son and then to his co-worker. Of 6 sporadic cases, 3 acquired their infection overseas (in Indonesia, Cambodia and Vietnam, respectively), and 3 cases acquired their infection in WA, with source unknown. Vaccination status was unknown for 9 cases, 2 were fully vaccinated, and 4 were unvaccinated. There were no cases of congenital rubella in 2011.

Mumps activity remained low in 2011, with 14 notifications, primarily adults living in the Perth metropolitan area. There was only one notification of invasive Haemophilus influenzae type b (Hib) infection in 2011—a 17-month old non-Aboriginal child who had received 4 doses of vaccine.

The number and rate of notifications of invasive pneumococcal disease (IPD) increased significantly over the past 2 years from 150 cases (6.8 per 100,000 person-years) in 2009 to 244 cases (10.4/100,000) in 2011. The increase was mostly due to a more than 3-fold increase in cases in Aboriginal people, from 34 to 117 cases (156/100,000), the highest number and rate on record. Although the IPD notification rate due to serotypes covered by the 7-valent conjugate pneumococcal vaccine declined steadily from 2001 to 2011 (from 7/100,000 to 0.4/100,000 person years) the rate due to serotypes not present in this vaccine, but contained in the 23-valent vaccine, increased from 1.8/100,000 to 7.8/100,000 person years. In 2011, these increases were particularly seen in Aboriginal people for serotypes 1 (38% of Aboriginal cases) and 12F (12%). Among non-Aboriginal people, serotype 19A was the most common serotype (31% of cases). The new 13-valent conjugate pneumococcal vaccine (Prevenar 13) covers serotypes 1 and 19A and is expected to result in a decline in IPD caused by these serotypes.

Varicella-zoster virus notifications for all 3 categories of chickenpox, shingles, and unspecified laboratory-confirmed cases, increased each year from 2007 to 2011. The age groups with the highest notification rates in 2011 were the 5 to 9 years group for chickenpox, and the 55 to 59 years group for shingles.

There was one tetanus notification in 2011: an elderly woman who became symptomatic following a rose-thorn prick to her leg, and who had no record of receiving tetanus vaccine.

Vector-borne diseases

Notifications of both Ross River virus (n=884) and Barmah Forest virus (n=156) each increased in 2011, to levels typical of high virus activity years. Notification rates for Ross River virus infection were highest in the Kimberley, Pilbara, Southwest, Great Southern and Wheatbelt regions (as shown in Figure 2), while Barmah Forest virus was most frequently notified from the Kimberley and Midwest regions.

Figure 2:  Number and rate of notifications of Ross River virus infection in Western Australia by region, 2011.

Figure 2: Number and rate of notifications of Ross River virus infection in Western Australia by region, 2011.

There were 9 cases of Murray Valley encephalitis reported in 2011—the largest number since 2000. There were no cases notified in 2010. Cases acquired their infections in an area stretching from the Kimberley region in the north to Carnarvon—and possibly the Murchison area—in the south, and east to the Goldfields region’s border with the Northern Territory. One case died and others have long-term neurological sequelae. The occurrence of the human infections corresponded with widespread seroconversions in sentinel chicken flocks.

Following the dramatic increase to 509 cases in 2010, the number of dengue fever notifications decreased to 327 cases in 2011 but was still more than double the 134 cases notified in 2009. All cases were acquired overseas, the vast majority in Bali (86%). This follows annual increases in the number and proportion of Bali-acquired infections from a mean of 2 cases per year (14% of all dengue cases) in the period 2001–2006 to 35%, 44%, 65% and 82% of notified cases in 2007, 2008, 2009 and 2010, respectively. The estimated notification rate for dengue fever among WA air travellers to Bali increased from 3 to 81 cases/100,000 passengers between 2005 and 2011. Serotype data available from 2011 shows that all 4 dengue virus serotypes circulate in Bali, although serotype 1 predominated, comprising 40% of cases.

There were 4 chikungunya virus notifications in 2011, acquired in Indonesia (n=2), Vietnam and North Africa. Malaria notifications (n=64) were lower than the previous 4-year mean (n=78), with infections all acquired overseas, mainly in African countries.

Schistosomiasis notifications declined yearly in the 5 years to 2011, from 357 in 2007 to 114 in 2011. In 2011, all infections were acquired overseas, primarily in African and Middle Eastern countries (89% of cases). Changing patterns of migration, particularly a reduction in the number of persons coming from Africa under the humanitarian entrant program, accounted for the overall decline in notifications.

The number of rickettsial infections, including typhus, in 2011 (n=38), was nearly triple that of the previous year (n=13), due to a large increase in overseas-acquired cases (from 9 in 2010 to 24 in 2011). The 3 main travel countries were Indonesia (n=8), Thailand (n=4) and Malaysia (n=3). Overseas-acquired infections included murine typhus (38%), scrub typhus (33%) and spotted fever group rickettsioses (29%). Of the 5 infections acquired in WA, there was one case each of murine typhus and scrub typhus, the latter following travel in the Kimberley region, and 3 spotted fever group infections.

Zoonotic diseases

Notifications for brucellosis, leptospirosis, psittacosis and Q fever continue to be infrequent. One case of brucellosis was reported in 2011, following travel to Iraq. The 2 reported cases of leptospirosis were associated with overseas travel, to Thailand and Indonesia, respectively. One of the 6 reported cases of psittacosis in 2011 was acquired in Vietnam but 5 cases were acquired locally and all kept pet birds at home. There were 10 notifications of Q fever, one associated with travel to China. Of the 9 locally acquired infections, 7 had occupational exposures too livestock and 2 cases did not have obvious direct exposures.

Blood-borne viral diseases

There were 18 “newly acquired” hepatitis B notifications in 2011, which was 55% lower than the previous 4-year mean of 42 notifications per year. In 2011 the notification rate for males was twice that of females. The number of “unspecified” hepatitis B notifications (n=662) was similar to the previous 4-year mean (n=688). The Kimberley region had the highest notification rate of “unspecified” hepatitis B—6 times the state rate—but 79% of the notifications attributed to the Kimberley were among asylum seekers detained on Christmas Island or in the Curtin Immigration Detention Centre near Derby. Immigration detainees are systematically screened as part of arrival health checks, and usually originate from countries where hepatitis B is endemic.

In 2011 there was a 33% increase above the previous 4-year mean in the number of “newly acquired” hepatitis C notifications (n=116). Most of the increase was accounted for by 51 new cases in 2011 diagnosed through screening in correctional facilities, compared to 26 cases in 2010. “Unspecified” hepatitis C notifications declined by 13% in 2011 (n=971) when compared to the mean of the previous 4 years. The “unspecified” hepatitis C notification rate for males in 2011 was more than double the rate for females.

Sexually transmissible infections

There were 11,762 notifications of genital chlamydia in 2011, 15% more than in 2010, which followed an increase in chlamydia notifications each year from 1993 when chlamydia became a notifiable disease. As in previous years, a higher percentage of notifications overall were for females (58%), but this was not uniform across age groups, with females more commonly notified than males in those aged under 25 years, whereas the converse was true in older individuals. The age group with the highest notification rate was the 20 to 24 year group (2,402 cases per 100,000 population). The notification rate for chlamydia was 5.4 times higher in Aboriginal people compared to non-Aboriginal people, and largely reflecting this differential, notification rates were highest in the Kimberley, Pilbara, Goldfields and Mid West regions.

Gonorrhoea notifications in 2011 (n=1,840) increased by 31% compared to 2010 levels (n=1,405), and were higher in 2011 than for any of the previous 4 years, reversing a steady decline over that period. In 2011 the notification rate for gonorrhoea was markedly higher (70 times) in Aboriginal people compared to non-Aboriginal people. There was a 38% increase in notifications for Aboriginal people from 2010 (n=834) to 2011 (n=1153), and this accounted for most of the overall increase in notifications. Aboriginal cases were evenly spread by gender, but a higher percentage of non-Aboriginal cases were male (74%). The notification rate was highest in the Kimberley region (1,631/100,000 population), which also experienced the greatest increase in number of notifications from 2010 to 2011 (see Figure 3). The highest notification rates in 2011 were in the 15 to 19 year (305 per 100,000 population) and 20 to 24 year (274/100,000) age groups.

Figure 3:  Number of gonorrhoea notifications in Western Australia by region, 2010 and 2011.

Figure 3: Number of gonorrhoea notifications in Western Australia by region, 2010 and 2011.

Infectious syphilis notifications increased by 52% from 2010 (n=83) to 2011 (n=126). In 2011 the notification rate for Aboriginal people was 9.5 times the rate for non-Aboriginal people. For non-Aboriginal people, the majority of notifications were in males (92%) whereas for Aboriginal people notifications were more evenly spread by gender (56% male). The highest notification rates were in the 25 to 29 year and 20 to 24 year age groups (rates of 13.0/100,100 and 11.7/100,100 population, respectively). Notification rates were highest in the Kimberley and Goldfields regions. However, most of the increase in notifications between 2010 and 2011 was in the metropolitan regions, primarily in non-Aboriginal men who have sex with men. The number of non-infectious syphilis notifications in 2011 (n=98) was similar to the previous 4-year mean (n=104). There were no cases of congenital syphilis in 2011.

No cases of donovanosis or chancroid were reported in 2011.

After reaching a record peak of 113 cases in 2010, annual notifications of human immunodeficiency virus (HIV) infection decreased marginally to 106 cases in 2011. There were 72 (68%) male cases (median age 40 years) and 34 (32%) female cases (median age 30 years), and most cases resided in the Perth metropolitan area (92%). The distribution of exposure groups was similar to previous years, with the majority of cases (95%) reporting sexual contact as the most likely route of transmission. Of the male cases, over half (56%) reported sex with men, 36% reported heterosexual exposures and 8% reported other or unknown exposures. Most female cases reported heterosexual contact (85%) and 15% reported other or unknown exposures. Of the heterosexually acquired male and female cases, 46% and 69%, respectively, were born overseas and also acquired their infection overseas, generally in the region of their birth. The number of people reporting transmission via injecting drug use remained low (3 cases). There were 5 new cases of HIV infection among Aboriginal people, and most reported heterosexual exposure (4 cases) and resided in the non-metropolitan regions (4 cases).

Other diseases

There were 20 acute rheumatic fever notifications in 2011, the same number as in 2010. With one exception, all cases were Aboriginal people, and all but 2 lived in remote areas of the state. The age range for cases was 5 to 29 years (median 10 years).

The number of invasive meningococcal disease notifications in 2011 (n=22) was similar to the previous 4-year mean (n=24). The majority of infections were due to serogroup B organisms (20 cases); and 2 were serogroup Y. The highest notification rates were in the 0 to 4 year and 15 to 19 year age groups (rate 2.5 cases/100,100 population in both groups). There were 2 deaths in 2011, both in middle-aged adults with serogroup B infection.

There was a 23% increase in legionellosis notifications in 2011 (n=80) above the previous 4-year mean (n=65). As is typical for WA, the majority of infections were due to Legionella longbeachae (72%), which is associated with exposure to gardening soils and potting mixes, and the remainder were caused by L. pneumophila, associated with spray mists from warm water sources such as air conditioning cooling towers, spas, fountains and hot water systems. Four of the 14 L. pneumophila cases notified in 2011 were part of an outbreak that started in 2010, and was associated with a particular hotel in Kuta, Bali, Indonesia. Further cases associated with this hotel, or a nearby exposure source, were identified in Victorians and Europeans.

Tuberculosis (TB) notifications increased each year from 2007 (n=60) to 2011 (n=124), due to increasing numbers of overseas-born cases, from 54 in 2007 to 112 in 2011. Of 12 Australian-born cases in 2011, 6 acquired their infection in WA. Four of the 2011 cases had multi-drug resistant TB and 4 were relapses.

Four cases of meliodosis were notified in 2011, with an age range of 59 to 63 years. Two cases appeared to have been acquired overseas, in Thailand and Vietnam respectively, and the other 2 cases were acquired in the Northern Territory. A single case of leprosy was notified in 2011, in a student from Nepal.

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