Delivering a Healthy WA
Disease WAtch

Review of notifiable infectious diseases, Western Australia, 2012

Western Australia had 34,161 communicable disease notifications in 2012, a 12% increase on the number of notifications in 2011, and the highest number on record. This increase was due largely to an additional 3379 influenza notifications in 2012, and smaller increases in the number of Ross River virus, gonorrhoea, dengue fever, hepatitis B and rotavirus notifications.

The most frequently notified diseases in 2012 were genital chlamydia (11,878 cases), influenza (5,266), pertussis (3,388), varicella-zoster infection (2,497), gonorrhoea (2,128), campylobacteriosis (1,928), Ross River virus infection (1,377), and salmonellosis (1,177).

Enteric diseases

With the exception of rotavirus, the number of notifications for all enteric diseases declined or remained stable in 2012, compared to 2011.

The number of notifications for campylobacteriosis (n=1928) and cryptosporidiosis (n=168) in 2012 were 14% and 32% lower respectively, than the mean of the previous 4 years, while the number of salmonellosis notifications (n=1,177) was similar to the previous 4-year mean.

Rotavirus notifications rose 87% in 2012 (n=351) compared to 2011 although this was still lower than the previous 4-year mean (n=414). The majority of cases (61%) were in the 0–4 year age group, and of those 52% were fully vaccinated for this disease.

The number of shigellosis notifications in 2012 (n=53) was lower than in any of the previous 4 years, reflecting in particular a continuing decline in Shigella flexneri notifications among Aboriginal people in the Kimberley and Pilbara regions.

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. The Kimberley region had the highest notification rates in the State for the more frequently notified enteric diseases. For most enteric infections, notification rates were also higher for Aboriginal people than non-Aboriginal people. The greatest difference was for shigellosis, for which the notification rate for Aboriginal people was 10 times that of non-Aboriginal people.

In 2012, hepatitis A notifications were 45% lower (n=14) than the historical 4-year mean, with notification numbers lower for both WA and overseas-acquired cases.

Of 8 cases of listeriosis notified in 2012, only 1 was related to pregnancy. The organism was isolated from the mother and the baby survived. The other cases involved middle-aged or elderly people, most of whom had one or more chronic medical condition that predisposed them to Listeria infection.

Typhoid (n=18) and paratyphoid (n=9) fever notifications were higher in 2012 than the previous 4-year means. All but 1 case acquired infection during overseas travel, mostly in Indonesia and India. The single apparent locally acquired infection was in an overseas-born person who was believed to be a chronic carrier, as S. Typhi was isolated repeatedly from their urine.

Vibrio parahaemolyticus notifications were also higher than the previous 4-year mean, due to an increase in overseas-acquired infections. The majority of cases (79%) were acquired overseas, mostly in South-East Asian countries—Thailand (4), Indonesia (3) and Malaysia (2).

One case of hepatitis E was notified in 2012, with infection acquired in Turkey.

Gastrointestinal disease outbreaks

There were 14 significant outbreaks of food-borne or suspected food-borne disease investigated in WA in 2012.

Of these, 4 were caused by Salmonella species, 1 each by Listeria and Campylobacter, 2 by norovirus, while for 6 outbreaks the infectious agent or toxin was not identified. The largest food-borne outbreak in 2012 was caused by Salmonella Typhimurium PFGE type 0039, with 128 cases notified. Most cases had consumed chicken prior to illness and chicken meat samples were positive for the same type of Salmonella.

Other Salmonella outbreaks were associated with eating salad from a takeaway outlet (4 cases), raw almonds produced in Australia (6 WA cases that were part of a multijurisdictional outbreak), and unknown food from a restaurant (4 cases). The Campylobacter outbreak, with 4 bacteriologically proven cases amongst a much larger number of ill patrons, was associated with eating chicken pate at a restaurant. The 2 norovirus outbreaks were thought to be due to food contaminated by ill food handlers. There was 1 identified case of Listeria infection in WA associated with a multijurisdictional outbreak of listeriosis caused by contaminated soft cheeses from a Victorian manufacturer.

There were 113 non-food-borne gastroenteritis outbreaks reported in WA in 2012, 45% higher than in the previous year. The causative agent for 68% (n=76) of these outbreaks was confirmed as norovirus, and rotavirus was the cause of 3 outbreaks. Non-food-borne outbreaks were predominantly associated with institutional settings, particularly residential care facilities (71%) and hospitals (20%).

Vaccine-preventable diseases

The pertussis epidemic that began in mid-2011 began to decline at the beginning of 2012 (Figure 1). In 2012, there were 3,388 pertussis notifications, 16% fewer than in 2011, but still twice the previous 4-year mean (n=1,684).

Figure 1 – Number of pertussis notifications in Western Australia by month, 2011 to 2012

Pertussis notification rates were highest in the 0–4 year age group (292 per 100,000 population), followed closely by the 10–14 and 5–9 year age groups (264 and 259 per 100,000, respectively). The decline in notifications from 2011 to 2012 was most evident in the 5–9 year and 10–14 year age groups (Figure 2). Notification rates were lowest in older teenagers and young adults, and increased again in middle-aged and older adults. Pertussis notification rates were highest in the Kimberley and Midwest regions, while the Goldfields and Wheatbelt regions had significantly lower rates than the rest of the State.

Figure 2 – Pertussis age-specific notification rates in Western Australia by year, 2011 and 2012

In 2012, there were 5,266 influenza virus notifications, similar to the number of notifications during the influenza pandemic of 2009. Influenza A/H3N2 and B subtypes comprised 48% and 37% of cases respectively, and only 0.5% of notified cases were attributed to A/H1N1(2009). Notification rates were highest in the Kimberley and Midwest regions and lowest in the Southwest region. The 2012 influenza season in WA commenced relatively early, with a sharp rise in activity that impacted significantly on health services—27% (n=1,420) of notified cases were hospitalised, the majority of whom were children aged 0-9 years (n=326, 23%) and older people aged 60 years and over (n=556, 39%). At least 33 deaths were associated with notified influenza in 2012.

There has been no endemic measles transmission in WA since the late 1990s, and the number of measles notifications remains low, associated mostly with importation from overseas and occasional limited local transmission. There were 6 measles cases in 2012; 4 of these were acquired overseas, in Thailand (n=3) and Pakistan (n=1), while the remaining 2 cases were acquired in WA from siblings who were infected overseas.

The median age of measles cases was 33 years (range: 8 to 40 years); 1 was a fully vaccinated child, 3 cases were partially vaccinated, 1 case was not vaccinated and 1 case had unknown vaccination status.

There were 2 cases of rubella notified in 2012, both were unvaccinated males aged 24 and 32 years. One case acquired his infection in Bali, Indonesia. The source for the other case was not determined, although he worked with fly-in-fly-out workers from overseas. There were no cases of congenital rubella in 2012 – the last reported case was acquired overseas in 2001.

Mumps activity remained stable and low in 2012, with 19 notifications, primarily adults living in the Perth metropolitan area. Nine cases acquired their infections in WA, 8 infections were acquired overseas, mostly in South-East Asian countries, 1 infection was acquired interstate and the place of acquisition for 1 case was unknown.

There was only 1 notification of invasive Haemophilus influenzae type b (Hib) infection in 2012, in a 2 year old fully vaccinated Aboriginal child.

There were 235 invasive pneumococcal disease (IPD) notifications in 2012, slightly fewer than the record high of 244 cases in 2011, when the new 13-valent conjugate vaccine was introduced. The number of cases aged 0–9 years decreased sharply from 72 in 2011 to 32 in 2012, while there were increases in the adult age groups, particularly those aged 30–39 years (75% increase) (Figure 3). The number of IPD cases in non-Aboriginal people rose by 24% between 2011 and 2012 (from 127 to 157 cases). However, the number of cases in Aboriginal people declined by 33% (from 111 to 78 cases), largely due to a dramatic decline in infections caused by serotype 1 pneumococci (from 44 to 15 cases) which had caused an outbreak in 2011, mostly among Aboriginal people from remote regions of WA.

In 2012, only 8% of IPD cases (n=14) were due to serotypes covered by the 7-valent conjugate pneumococcal vaccine, 41% (n=96) were caused by the additional 6 serotypes in the 13-valent vaccine, 27% were due to serotypes in the 23-valent vaccine (excluding the 13-valent vaccine serotypes) and 21% were caused by serotypes not covered by any vaccine.

Figure 3 – Invasive pneumococcal disease notifications by age group, Western Australia, 2011 and 2012

Varicella-zoster virus notifications for chickenpox declined in 2012 after increasing over the previous 4 years. In contrast, notifications for shingles and unspecified laboratory-confirmed varicella-zoster infections, increased for the fifth consecutive year. The majority of chickenpox cases in 2012 were among children aged 0-14 years (73%), while shingles and unspecified varicella-zoster infections were more evenly distributed across all age groups.

There was 1 tetanus notification in 2012 which involved an elderly woman who had no record of receiving tetanus vaccine and was reported to have had a thorn injury.

Vector-borne diseases

Notifications for both Ross River virus (n=1,377) and Barmah Forest virus (n=216) increased in 2012. Ross River virus activity increased in late 2011 and peaked in the first quarter of 2012, declining thereafter (Figure 4). Notification rates for Ross River virus infection were highest in the Great Southern and Kimberley regions.

By contrast, the number of Barmah Forest virus cases began increasing in the fourth quarter of 2012 and reached record levels during 2013. The unexpected increase in Barmah Forest virus cases has been attributed to an increase in false positive laboratory test results, which are currently under investigation.

Figure 4 – Number of notifications of Ross River virus and Barmah Forest virus infections in Western Australia by year and quarter, 2011 and 2012

No cases of Murray Valley encephalitis virus or Kunjin virus infection were notified in 2012.

The number of dengue fever notifications rose by 64% in 2012 to reach a record high of 532 cases. All cases were acquired overseas, the vast majority in Bali (80%) and Thailand (11%). The proportion of Bali-acquired infections has increased from 14% of notified dengue cases in the period 2001–2006 (a mean of 2 cases per year) to 35%, 44%, 65%, 82% and 85% of notified cases in 2007, 2008, 2009, 2010, and 2011 respectively. The estimated notification rate for dengue fever among WA air travellers to Bali increased from 3 to 100 cases per100,000 passengers between 2005 and 2012.

There were 4 chikungunya virus notifications in 2012, all acquired in Bali, Indonesia. There were 51 malaria notifications, the lowest number in 5 years, with infections all acquired overseas, mainly in African countries.

Schistosomiasis notifications have declined progressively from 337 cases in 2008 to 86 cases in 2012. In 2012, all infections were acquired overseas, primarily in African countries (97% of cases). The decline in notifications is attributed to a decrease in the number of immigrants and refugees arriving from endemic areas.

The number of rickettsial infections, including typhus, decreased in 2012 (n=33), but was 42% higher than the previous 4-year mean. Of the 33 cases, 18 (55%) were acquired overseas, mostly in Indonesia (n=13) and 11 were acquired in Western Australia, while for 4 cases, place of acquisition was unknown. Overseas-acquired rickettsial infections included murine typhus (56%), scrub typhus (22%) and spotted fever groups (22%). The 11 WA-acquired infections included 1 case with murine typhus, 4 with spotted fever group infections, and 6 cases with ambiguous serology.

Zoonotic diseases

Notifications for brucellosis, leptospirosis, psittacosis and Q fever continue to be infrequent. The single case of brucellosis reported in 2012 was acquired in Iraq. There were 4 reported cases of leptospirosis; 2 cases were locally-acquired, in an abattoir worker and a farmer, and 2 cases were associated with overseas travel, to Thailand and Laos, respectively.

There were 8 psittacosis notifications in 2012, of which 1 case was acquired overseas, in Bali. Of the 7 locally-acquired cases, most kept birds at home. There were 7 notifications of Q fever, the place of acquisition could not be determined for 1 case and 6 were locally-acquired infections—1 worked at an abattoir, 1 with cattle, 1 reported contact with feral goats, 3 cases did not have obvious livestock exposures and the exposure history for 1 case was not determined.

Blood-borne viral diseases

There were 24 “newly acquired” hepatitis B notifications in 2012, 29% lower than the previous 4-year mean of 34 notifications per year.

The number of “unspecified” hepatitis B notifications increased by 28% in 2012 (n=813) and was 19% higher than the previous 4-year mean. The increase was due largely to 234 (29%) notifications among illegal marine arrivals (IMAs) detained on Christmas Island or in the Curtin Detention Centre near Derby. Notifications for these centres are attributed to the Kimberley region, which as a consequence had the highest “unspecified” hepatitis B notification rate – 21 times the state rate. IMAs are screened for hepatitis B and other infections as part of arrival health checks, and usually originate from countries where hepatitis B is endemic.

In 2012, there were 124 “newly acquired” hepatitis C notifications, a 29% increase on the previous 4-year mean. The “newly acquired” hepatitis C notification rate for males was more than double that of females in 2012. “Unspecified” hepatitis C notifications increased marginally in 2012 (n=1028) compared to 2011 but were 4% lower than the previous 4-year mean (n=1073).

There were 2 notifications of hepatitis D in 2012.

Sexually transmissible infections

The number of genital chlamydia notifications plateaued in 2012 (n=11,878), although this was still 20% higher than the previous 4-year mean (n=9,886). As in previous years, a larger proportion of notifications were female (58%), although this was not consistent 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 20 to 24 year age group had the highest notification rate (2,396 notifications per 100,000 population). The chlamydia notification rate was 4 times higher in Aboriginal people compared to non-Aboriginal people. Reflecting this differential, notification rates were highest in the Kimberley, followed by the Goldfields, Pilbara and Midwest regions.

Gonorrhoea notifications increased in 2012 for the third consecutive year, to 2,128 cases, the highest number on record, and 36% higher than the previous 4-year average (n=1,571). Notifications for non-Aboriginal people increased by 45% between 2011 (n=659) and 2012 (n=957), accounting for most of the overall increase. The number of gonorrhoea notifications for Aboriginal people was stable in 2012, although the notification rate remained markedly higher (29 times) compared to non-Aboriginal people (1,132 versus 40 cases per 100,000 population). The majority of non-Aboriginal cases were male (71%) while the Aboriginal cases were fairly evenly spread across the sexes (47% male). The North Metropolitan region had the largest increase in the number of cases in 2012, followed by the Kimberley and South Metropolitan regions (see Figure 5). The Kimberley region had by far the highest notification rate in 2012 (1,778 cases per 100,000 population). In terms of age, notification rates were highest in the 15 to 24 year age group (352 per 100,000 population).

Figure 5 – Number of gonorrhoea notifications in Western Australia by region, 2011 and 2012

Infectious syphilis notifications decreased by 34% from 2011 (n=121) to 2012 (n=80). Both Aboriginal and non-Aboriginal cases declined in 2012, the former by 50% (from 26 to 13 cases) and the latter by 29% (from 95 to 68 cases). The notification rate for Aboriginal people in 2012 was 5.8 times the rate for non-Aboriginal people (16.9 versus 2.9 cases per 100,000 population). For non-Aboriginal people the majority of notifications were in males (97%), whereas among Aboriginal people notifications were spread evenly by gender (54% male). The highest notification rates were for the 25 to 34 years and 35 to 44 year age groups (both 6.3 per 100,000 population). Notification rates were highest in the Kimberley and Goldfields regions. The number of non-infectious syphilis notifications in 2012 (n=137) was 42% higher than the previous 4-year mean (n=96). There were no cases of congenital syphilis notified in 2012.

No cases of chancroid were reported in 2012, and there was 1 locally-acquired case of donovanosis in a non-Aboriginal person with a partner from overseas.

Annual notifications of human immunodeficiency virus (HIV) infection reached a record peak of 121 cases in 2012, increasing from 105 cases in 2011. There were 94 (78%) male cases (median age 39 years) and 27 (22%) female cases (median age 33 years), and most cases resided in the Perth metropolitan area (85%). The distribution of exposure groups was similar to previous years with the majority of cases (97%) reporting sexual contact as the most likely route of transmission. Of the male cases, over half (58%) reported sex with men, 38% reported heterosexual exposures and 2% (2 cases) reported injecting drug use as their only risk factor. Most female cases reported heterosexual contact (96%) and 4% other or unknown exposures.

Of the heterosexually acquired male and female HIV cases, 46% and 67%, respectively, were born overseas and also acquired their infection overseas, generally in the region of their birth. Australian-born males who acquired HIV overseas made up 38% of heterosexually acquired male cases, with most of these men acquiring their infection in South-East Asia. The number of people reporting transmission via injecting drug use remained low (2 cases). No new cases of HIV infection were reported among Aboriginal people in 2012.

Other diseases

There were 62 acute rheumatic fever notifications in 2012, almost triple the number in 2011. All cases were Aboriginal people, and all but 5 lived in remote areas of the state. The age range for cases was 3 to 44 years (median age 10 years). It is unclear to what extent the increase reflects a true increase in disease incidence, versus improved case ascertainment and/or notification.

The number of invasive meningococcal disease notifications in 2012 (n=19) was 21% lower than the previous 4-year mean (n=24), and the lowest number recorded in over 20 years. The majority of infections were due to serogroup B organisms (15 cases), 2 were serogroup C, 1 was serogroup Y and 1 was untyped. The largest proportion of cases was in the 0 to 4 year age group (26%), followed by the 20 to 24 year age group (21%). There were 3 deaths in 2012—2 cases aged 1 and 23 years had serogroup B infections, while the third, who was 94 years old, had serogroup C disease.

There were no notifications for haemolytic uraemic syndrome in 2012 and 3 notifications for Creutzfeldt-Jakob disease.

Legionellosis notifications increased for the third consecutive year in 2012 (n=87) and were 36% above the previous 4-year mean (n=64). The majority of infections were due to Legionella longbeachae (85%), 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. Of the 13 L. pneumophila cases notified in 2012, 4 were acquired overseas; 3 in Bali, Indonesia and 1 in Thailand. The 3 Bali-acquired cases were notified a month or more apart and stayed at different hotels. One of these cases stayed at the same hotel in Kuta, Bali that was associated with an outbreak in Australian travellers that started in 2010 and extended into 2011.

Tuberculosis (TB) notifications have increased each year from 2008 (n=95) to 2012 (n=172), due to increasing numbers of overseas-born cases, from 88 in 2008 to 158 in 2012. Of the 14 Australian-born cases in 2012, 4 acquired their infection in WA. Three cases notified in 2012 had multi-drug resistant TB and 3 of the cases were relapses.

Three cases of meliodosis with an age range of 62 to 85 years were notified in 2012. All were acquired in Western Australia, 2 in the Kimberley region and 1 seemingly in the outer Perth metropolitan area. No cases of leprosy were notified in 2012.

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