Describe disease surveillance.

Disease Surveillance

• Its objectives — to detect outbreaks early; to monitor trends in disease; to identify populations at risk; to evaluate control programmes; to plan and allocate resources; to monitor changes in the agent, such as antimicrobial resistance and serotype shift; and to generate hypotheses for research
• The types:
• Passive surveillance — reports flow IN from health facilities as a matter of routine. It is cheap and covers a wide area, but is incomplete, delayed and of variable quality, and is what most routine reporting systems consist of
• Active surveillance — the health authority actively seeks out cases, by contacting facilities, reviewing records or searching the community. It is far more complete and timely but expensive, and is used during outbreaks and in eradication programmes — as in the weekly active search for acute flaccid paralysis under the polio programme
• Sentinel surveillance — using a selected sample of reporting sites to give high-quality, timely data at the cost of complete coverage; useful for influenza and for antimicrobial resistance
• Syndromic surveillance — monitoring clinical syndromes rather than confirmed diagnoses (acute watery diarrhoea, fever with rash, acute flaccid paralysis), which permits earlier detection before laboratory confirmation and is the basis of IDSP
• Sentinel event (avoidable death) surveillance, in which a single occurrence signals a system failure — a maternal death being the standard example
• The attributes of a good surveillance system, which are examined as a list — simplicity; flexibility; acceptability to those who must report; sensitivity; positive predictive value; representativeness; timeliness; stability; and data quality
• There is an inevitable tension between completeness and timeliness, and for outbreak detection timeliness matters more — a rough figure today is worth more than a precise one next month
• The other unavoidable tension is that complex systems collect better data and are abandoned by those asked to fill in the forms; simplicity is therefore not a minor virtue
• Notification of disease is the statutory backbone — a legal obligation on the medical practitioner to report specified diseases. Under the international health regulations (2005), countries must notify WHO of any event that may constitute a public health emergency of international concern, with smallpox, wild poliovirus, new influenza subtypes and SARS notifiable unconditionally
• IN INDIA the principal system is the integrated disease surveillance programme (IDSP), established in 2004 and now operating through the IHIP (Integrated Health Information Platform)
• It collects data on three forms — S (syndromic), reported by health workers; P (presumptive), reported by medical officers; and L (laboratory), confirmed
• Its structure — surveillance units at central, state and district level, with a district as the operational unit; rapid response teams; a referral laboratory network; and weekly reporting with analysis for outbreak signals
• Other Indian systems — the sample registration system for vital rates; programme-specific surveillance for tuberculosis (Ni-kshay), HIV, malaria and leprosy; AFP surveillance for polio; cancer registries; and AEFI (adverse events following immunisation) surveillance
• The persistent weaknesses that should be stated honestly — under-reporting, particularly from the large private sector, which treats the majority of Indian patients; incomplete laboratory confirmation; delayed reporting; data collected but not analysed or fed back; and weak linkage between surveillance and response
• Feedback to those who report is the most neglected element and the most important for sustaining a system, because people who never see their data used soon stop sending it
• Surveillance is information for action, and data never fed back or acted on is merely collection
• Feedback sustains a reporting system; people who never see their data used soon stop sending it
• Timeliness beats completeness for outbreak detection, since a rough figure today is worth more than a precise one next month
• Simplicity is not a minor virtue; complex systems collect better data and are abandoned by those filling the forms
• Passive surveillance is cheap and incomplete while active surveillance is complete and expensive
• Syndromic surveillance detects earlier than laboratory confirmation, which is why IDSP is built on it
• Sentinel sites trade coverage for quality, and suit influenza and antimicrobial resistance monitoring
• A single maternal death is a sentinel event, signalling a system failure rather than an individual misfortune
• Under-reporting from the private sector is the largest gap in Indian surveillance, since it treats most patients
• The S, P and L forms of IDSP are syndromic, presumptive and laboratory-confirmed respectively
• The district is the operational unit of IDSP, with rapid response teams and a referral laboratory network
• The International Health Regulations require notification of any event that may be a public health emergency of international concern
• Active AFP surveillance underpinned polio eradication, and is the standard example of active case-finding