Surveillance and burden of infectious diseases in Australia

BACKGROUND: The epidemiology and comparative burden of communicable diseases determines which diseases warrant public health resources and intervention. Public health surveillance data are useful but are affected by variable case ascertainment. Disability Adjusted Life Years (DALYs) better define the population burden of diseases accounting for both morbidity and mortality. METHODS: Infectious disease notification practices in Victoria were examined using case notification data from 2013. Data for all nationally notifiable diseases were used to evaluate the first 21 years (1991–2011) of the National Notifiable Diseases Surveillance System (NNDSS) and the epidemiology of nationally notifiable diseases. The impact of socioeconomic disadvantage and remoteness of residence on notification incidence was examined nationally, while Indigenous status was examined in three jurisdictions with completeness of Indigenous status reporting >75% (the Northern Territory, South Australia and Western Australia). Disease burden was estimated and compared for six common gastrointestinal pathogens (campylobacteriosis, salmonellosis, cryptosporidiosis, giardiasis, rotavirus, and norovirus) in Australia in 2010 using: number of cases, number of deaths, and DALYs. Post-infectious sequelae were incorporated into DALY estimates for campylobacteriosis and salmonellosis. RESULTS: Almost half (49%) the cases notified in Victoria in 2013 were notified by laboratory report alone. Indigenous status was complete for 48% of notified cases, with higher completion of Indigenous status among doctor-notified cases, diseases with active case follow-up, and priority diseases for Indigenous status reporting. Nationally, the number of notifiable conditions increased from 37 to 65 from 1991 to 2011, with 2.4 million cases notified to NNDSS. An increasing proportion of cases were diagnosed by PCR, while data completeness and notification timeliness improved. The 10 highest notification incidence conditions (chlamydial infection, campylobacteriosis, varicella zoster, hepatitis C, influenza, pertussis, salmonellosis, hepatitis B, gonococcal infection, and Ross River virus infection) comprised 88% of all notifications. Annual notification incidence increased 6·4% per year (12% for sexually transmissible infections and 15% for vaccine preventable diseases). Notification incidence was higher for Indigenous, remote-living and socioeconomically disadvantaged Australians; overall, these inequities lessened over the study period. An estimated 16.6 million acute gastroenteritis (AGE) cases occurred in Australia in 2010 (including undiagnosed community cases), with the most AGE cases attributed to norovirus (2,180,145), most deaths to salmonellosis (90), and most DALYs to campylobacteriosis (18,222). Inclusion of irritable bowel syndrome increased the DALY estimate for campylobacteriosis more than four-fold. CONCLUSIONS: The NNDSS expanded over its first 21 years including a greater number of notifiable conditions and notifications received. Changing testing practices and laboratory-only notifications have impacted notification practices. A nationally integrated electronic surveillance system, including electronic laboratory reporting, would further improve infectious diseases surveillance in Australia. Inadequate completeness of Indigenous status needs urgent attention, as does reducing the identified health inequities. The choice of burden of disease metric influenced the ranking of pathogens. Data on post-infectious sequelae is lacking for many gastrointestinal pathogens and their inclusion can profoundly influence DALY estimates. Routinely collected surveillance data and more detailed DALY estimates can both be used to prioritise diseases and populations for public health action and to assess the effectiveness of these interventions.