• public health surveillance
• Speaker's corner

Public health surveillance has been defined as the ongoing collection, analysis, and interpretation of health data essential to public health practice, closely integrated with timely dissemination of information for intervention. This is analogous to a 24 hour surveillance camera (data collection) under the watchful eyes of guards (data analysis and interpretation) who have telephone access (information dissemination) to the police and firefighters (intervention).

Two unique characteristics differentiate a surveillance system from other data systems, such as surveys, routine records, or research databases: surveillance is ongoing and linked to intervention. A smoke detector switched off intermittently offers unreliable protection. A sensor connected with a lamp provides automatic light when the night falls.

There are many uses of a public health surveillance system. It may monitor current status, just like a fridge thermometer, a bathroom scale, a mirror, or a photograph. It may document trend, similar to a videotape or a photo album. While a snapshot shows the status, a photo album shows the trend (changes over time). It may provide early warning, like a carbon monoxide detector. It may stimulate research, like a leaking roof. Detection devices, such as a smoke detector or a light sensor, collect data, but will not serve the intervention purpose unless they are linked respectively with a water sprinkler or a lamp. Finally, a surveillance system may evaluate interventions. This compares with a thermostat regulating a heating/cooling unit. When the thermostat detects excess heat, it turns on the cooling unit; on detecting excess cold air, it starts the heating unit.

Current use of surveillance data varies, and may be as rigid as a computer password, as specific as a cookbook, as general as manufacturer's recommendations, or as directional as a compass. Health surveillance systems still lack two features that characterise economic surveillance systems—the economic market index, and automated stock trading. An overall health index, based on composite indices, such as heart health, nutrition or health care utilisation indices, can be used to compare health trends over time and across jurisdictions. If major changes in the overall health index are detected, its composite indices can be examined to identify problems. In addition, warning levels and action levels should be established for public health decisions, as in automated stock trading.

Recently, surveillance systems have moved from the back pages to the front headlines. It is time for supportive health policy to reinforce surveillance as a frontline in public health.