Year in review: communicable disease surveillance, NSW, 2009

In this issue we present a review of notifiable diseases reported in New South Wales (NSW) residents in 2009. Conditions have been grouped into four categories (bloodborne viruses and sexually transmissible infections; enteric diseases; respiratory diseases; and vaccine-preventable diseases), with significant trends highlighted. Outbreaks of some diseases, notably chlamydia, cryptosporidiosis, H1N1 influenza and pertussis are discussed. For greater detail, refer to Tables 1–5, which show disease-specific data for notifications reported by: year of onset of illness; month of onset of illness; area health service; and age group and sex.

Highlights in 2009 included:

• Human immunodeficiency virus (HIV) infection: 328 cases were notified, reflecting a stable rate of infections in NSW. HIV infection continues to largely affect men who have sex with men, although in 2009 there was a small increase in the number of notifications of heterosexual people. Notifications associated with injecting drug use remained low, accounting for 3% of cases.

• Hepatitis C: 3951 cases were notified, similar to previous years. As hepatitis C infections are largely asymptomatic and cause chronic infections, caution should be used in interpreting these data as they may be influenced by changes in testing rather than in the incidence of the disease.

• Chlamydia: 14 998 cases were notified in 2009, the highest on record. Cases were most common in young adults, with more females than males notified in this age group likely reflecting higher screening rates in women.

• Infectious syphilis: 508 cases were notified, reflecting an ongoing outbreak, largely among men who have sex with men and who reside in inner Sydney.

• Gonorrhoea: 1653 notifications, mainly in men, were reported in 2009. Although this largely affected men who have sex with men, towards the end of 2009 there was a modest increase in the number of notifications in women.

The number of notifications of sexually transmissible infections continues to increase in NSW. Although this may in part be due to increased awareness and testing for these conditions, it demonstrates the continuing importance of prevention programs. The increases in sexually transmissible infections may threaten the current stability of the HIV epidemic in NSW.¹

Note that because of the chronic nature of hepatitis B and hepatitis C infection, repeat testing and repeat case notifications are common for these conditions. Recent improvements in methods for cleaning data have resulted in the identification of duplicate notifications of hepatitis B and hepatitis C cases. This has led to the reduction in the number of case notifications for previous years, particularly before 2005.

There were 6575 notifications of enteric disease in 2009, an increase of 39% compared with the average of the previous 5 years. This was largely due to an increase in notifications of cryptosporidiosis and shigellosis.

• There was a 147% increase of notifications of cryptosporidiosis (1484 notifications), compared to the annual average of 600 for the period 2004–2008. This was attributed to a large outbreak at the beginning of the year, associated with contaminated swimming pools.²

• There was a 63% increase in notifications of shigellosis (155 notifications) compared to the previous 5-year average of 95 notifications. Of these, 55% were seen in south-east Sydney. The majority (98%) of notifications in this area were male. Shigellosis in Sydney has been associated with men who have sex with men.³

• Salmonellosis (including infections caused by Salmonella Paratyphi) was the most frequently reported condition, with 2681 notifications, an increase of 20% compared to the previous 5-year average. An increase in S. Typhimurium 170 was seen nationwide and the cause of this increase was not identified.

• Of the 68 foodborne outbreaks seen in 2009, 24 (35%) were linked to Salmonella.

The outbreak of cryptosporidiosis reinforces the importance of keeping swimming pools free of infectious pathogens through awareness among patrons of not swimming within 2 weeks of experiencing diarrhoea, and pool operators maintaining high sanitary standards.

The numerous foodborne outbreaks emphasise the need for vigilance in the maintenance of safe food-handling practices.

Highlights in 2009 included:

• The emergence and outbreak of pandemic (H1N1) 2009 influenza which involved the most intensive public health response of recent years. Unpublished serological studies suggest that around 16% of the community had acquired the virus. People aged less than 65 years were much more likely to have acquired the infection than older people, with up to 35% of adolescents aged 12–17 years estimated to have acquired the infection. Once the pandemic was established in Australia, testing was only recommended where it would change clinical management or for surveillance purposes. In NSW, over 5000 cases were confirmed by laboratory testing. This underestimates the true incidence of disease. The outbreak peaked in mid-July, with approximately 1300 people presenting to emergency departments each week with influenza-like illnesses. In total 54 people died with confirmed pandemic (H1N1) influenza, although infection may have contributed to other deaths as well. Compared with previous outbreaks of seasonal influenza, pandemic (H1N1) 2009 caused much more illness in people under 60 years of age.⁴

• The number of cases of legionellosis remained steady in 2009 with 94 notifications. The last 2 years have seen more Legionella longbeachae than L. pneumophilia cases, a reversal of the historical distribution.

The emergence and substantial impact of pandemic (H1N1) influenza in 2009 reinforces the need for vigilance in the detection of emerging infections and for preparedness to manage such outbreaks. NSW Health continues to review the lessons learnt from the response to the pandemic to inform the revision of pandemic response plans for future implementation.

Highlights in 2009 included:

• In 2009, 12 578 notifications of pertussis were reported in NSW following a significant increase in 2008 (8759), and compared with 2100 notifications in 2007. While epidemics of pertussis occur every 3 to 5 years, notifications in 2008 and 2009 far exceeded previous epidemics. In 2009 the number of notifications increased in children aged less than 5 years (from 1206 notifications in 2008 to 2826 notifications in 2009); of these 86% had complete immunisation status. The highest increase in this age group was for those aged 3 years, which may reflect waning immunity following the primary course of immunisation at 2, 4 and 6 months of age and prior to receiving a booster dose at 4 years of age. In addition, the greater number of notifications in the 2009 epidemic compared with past epidemics may reflect more widespread use by laboratories of nucleic acid testing for pertussis, which is more sensitive than other methods for diagnosis.⁵

• Notifications of meningococcal disease have generally been declining in the past 10 years. A vaccine for serogroup C disease was added to the National Immunisation Program (in 2003) for children at 12 months of age. The vaccine was provided free to all children aged 1–19 years through schools and other programs. The greatest reduction in notifications over the subsequent years has been for meningococcal disease due to serogroup C, with seven cases reported in 2009. Notifications for other serogroups (B, W 135 and Y) have remained relatively stable.⁶

• There continued to be a decline in the rates of measles, mumps and rubella.

The outbreak of pertussis highlights the challenge of increasing vaccination rates among adolescents and young adults, as well as the importance of promoting and maintaining high vaccination rates in infants and their carers (Tables 1–5).

Table 1.  Disease notifications by year of onset of illness^a, NSW, 1992–2009

Table 2.  Disease notifications by month of onset of illness^a, NSW, 2009

Table 3.  Disease notifications by area health service of residence, crude rates per 100 000 population, NSW, 2009 (based on onset of illness^a)

Table 4.  Disease notifications by area health service of residence, NSW, 2009 (based on onset of illness^a)

Table 5.  Disease notifications by age group and sex of the case, NSW, 2009 (based on onset of illness^a)