Surveillance of communicable diseases

T here has been a resurgence of interest in communicable disease surveillance.Both State and Commonwealth Departments of Health are reviewing surveillance mechanisms for these diseases with the introduction in several States of laboratory-based reporting and an increased level of cooperation in the compilation of a national database. In 1980 a leading article in the Journal' discussed national reporting of communicable diseases, lamented the J:l,Qor rate of notification and proposed an improved system of data collection, analysis and interpretation. It was not the first call for an effective and truly Australian system of surveillance of communicable diseases. In 1884 the First Australian Intercolonial Sanitary Conference had recognised the same poor state of knowledge of the epidemiology of communicable diseases. The conference thought that information on the current state of public health was needed Australia-wide. It recommended: it is desirable that the various Governments should be accurately informed of the state of public health in the colonies respectively under their control; and that matters affecting the public health should be made known by each colony to every other. 2 The conference also recommended that all colonies should require practitioners to notify cases of communicable disease to health authorities. Victoria had been the first colony to require disease notification, obliging practitioners to report cases of smallpox under the Public Health Statute 1857 (Vic.). Over the next 50 years, under the influence of the British Public Health Act 1875, legal requirements for the notification of disease and for disease control measures were introduced throughout Australia. The legacy of this approach was significant differences in the lists of notifiable diseases and in administrative mechanisms between States. The National Health and Medical Research Council (NHMRC) in 1978 recommended a national list of notifiable diseases to be adopted by the States, yet a nationally consistent list has not been adopted by all States. Disease surveillance serves several purposes with the overall goal of contributing to disease control. Surveillance is chiefly intended to detect changes in the incidence of disease in order to initiate public health action, to evaluate the impact of disease control strategies and to enable forward planning of health services and infrastructure. In this issue of the Journal (page 828), Rushworth et al.3 report their experiences with a pilot project using information from microbiology laboratories in addition to practitioner notifications as a means of reporting communicable disease. They point out the low rate of notifications from practitioners and the frustrating lack of some elementary details on the notification forms. Frequently, notifications are sent too late to enable any useful action. The Laboratory Infectious Diseases Surveillance Project entailed the reporting by pathology laboratoriesof positive results of tests indicating the presence of causative organisms of notifiable diseases. Laboratory reporting produces a shift in the type of disease reported, since practitioner and laboratory reports represent different stages along the chain from disease onset to notification. Practitioner reports represent a clinical diagnosis or suspicion of disease and mayor may not be 9f confirmed cases. Laboratory reports represent the recognition of the presence of organisms which may be either pathogens or incidental findings. Some of the laboratory reports of pathogenic enteric viruses could have been from infants without clinically significant gastrointestinal disease with varying public health implications. As we have found with the Communicable Diseases Intelligence laboratory reporting scheme, it is very difficult to get reliable clinical data with laboratory reports, and laboratories cannot provide reports on cases diagnosed clinically. Laboratory reports only rarely distinguish between new and old cases; for example, positive tests for hepatitis B would represent old cases in most instances. However, coverage and timeliness are both greatly improved by the adoption of a laboratory-based system. Laboratory reports are generally more complete, in that laboratories can fairly readily and quickly supply information on all positive diagnostic tests. However, they are subject to specific biases. Most bias related to the selection of cases which are subject to laboratory diagnosis. Not all practitioners request laboratory diagnosis for cases of suspected notifiable disease; for instance, diagnostic serology is not routinely performed in this country for measles and laboratory reports may select only those atypical cases where the diagnosis is in doubt. These shortcomings aside, laboratory reporting of notifiable disease represents a major advance. Coverage is improved and biases can be allowed for in analysis. Bias is inherent in all surveillance systems and multiple approaches help clarify it. A system using both practitioner and laboratory notification as well as reports from "sentinel" practices will provide the most comprehensive information. Other steps can be taken to improve coverage and minimise bias by, for instance, providing easier means of notification with reply-paid forms or accepting telephone notifications. Communicable disease control, with the exception of quarantine, is the responsibility of the States and Territories, but many aspects of control are better addressed from a national perspective. This is because: (i) diseases cross State and Territory borders; (ii) there are common risk factors over the whole of Australia for communicable diseases; (iii) it is frequently more efficient to develop a single national approach, with consequent economies of scale; (iv) uncommon diseases may not be recognised as problems if viewed only from the perspective of a single State or Territory; (v) Australia requires a focal point for internationalliaison in communicable disease control; and (vi) expertise in Australia in all the areas required is limited and can be shared amongst all participants in the network.