Routine or passive surveillance

All health facilities collect data in their record keeping, at its simplest being the name, age and sex of the individual and the symptoms or diagnosis of their illness. Considerable use can be made of well-kept records and it is worth doing an analysis of the type of information collected to determine the best system to use with the resources available. Hospital records, while more detailed than in small clinics, will not be representative of the population.

Additional categories can be added to the basic data collected, but care must be taken not to overload the health staff so that an unreasonable amount of their time is taken up with filling in forms. Every additional entry must be tested by a small pilot study to ensure that it is collecting the information required and is within the means of the staff to collect it. If it is too onerous a task, then there will be a tendency to either not bother to collect the information or even worse, to falsify the data. Even the routine data already collected should be looked at in detail; for example, staff may record the number of patients reporting headaches, which will not be a valuable criterion. Recording fever rather than headache (and taking a blood slide) is far more useful.

Accuracy of data collection can be improved by training, with regular refresher courses so that all staff are taught the same method at the same time. Regular feedback of an analysis of the data will encourage staff to be vigilant in their returns. Comparing one area with another will show up weaknesses, which can then be strengthened. Formulating case definitions encourages a more consistent diagnosis.

Where facilities are available, laboratory confirmation is always desirable. Every fever case in a tropical area should routinely have a blood slide taken, and sputum smears always made from persons with a chronic cough. In special circumstances, having a screening programme can enhance routine investigations. Examples are antibiotic resistance patterns of STIs, Aedes aegypti index in dengue-susceptible areas, vaccine coverage in under-fives clinics and rainfall records to measure seasonality.

All data collected must be analysed or there is no point in collecting it in the first place. The well-established criteria of persons, place and time will be the basic model, but special techniques may also be required. Data from one level are sent to the next higher level where they are analysed, and a copy of the analysis sent both to the level above and to those collecting the data in the first place. Special reporting may be required for notifiable diseases. Evaluations need to be made at regular intervals to modify and improve the system.

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