Guidance

Zoonotic diseases: surveillance of laboratory confirmed cases

Updated 21 January 2019

1. National surveillance of laboratory-confirmed infections

Surveillance of laboratory-reported zoonotic infections is undertaken by Public Health England’s National Infection Service. National surveillance is maintained on several thousand species, subspecies and subtypes of microbial pathogens, of which zoonotic micro-organisms are a comparatively small proportion.

The following events must occur for data on a given case to be included in a national surveillance database for laboratory confirmed-infections:

• an infected individual must consult a clinician (GP or hospital doctor)
• the doctor must arrange for a specimen to be taken (faeces, blood etc.) and referred to a clinical microbiology laboratory
• the laboratory must detect and identify a micro-organism, or detect antibodies to an organism
• the laboratory must submit a report to the national surveillance centre

The national surveillance schemes for laboratory confirmed infections are not designed to provide direct measures of the numbers of cases of infection in the population caused by those pathogens under surveillance. A number of factors influence the degree of the disparity between the number of recorded laboratory reports for any given pathogen and the number of cases of infection in the population. These include:

• severity of disease
• duration of symptoms
• selectivity of screening protocols employed by diagnostic laboratories
• sensitivity of available diagnostic techniques

The severity of the disease and the duration of symptoms associated with infection dictate both the proportion of cases that consult clinicians, and the proportion of presenting cases from whom specimens are collected. They vary widely across the range of zoonoses under surveillance in the UK.

2. Sources of data

There are 3 main sources of data which together help to build a picture of the burden of zoonotic infection in the human population. These are:

• Notifications of infectious disease (NOIDS)
• National surveillance schemes for laboratory-confirmed infections
• Enhanced surveillance for specific zoonoses

Not all zoonotic diseases are notifiable under Public Health legislation. Recorded human cases represent only the ‘tip of the iceberg’ as many patients do not seek medical attention or, their doctor does not request laboratory investigation and, a positive result is either not notified or the occurrence of the disease is not notifiable. Reports may also be biased towards more clinically severe cases in high risk groups.

3. Notifications

Notifications relate to clinical disease, or to laboratory diagnosis. All doctors have a statutory duty to notify the proper officer of the local authority of all clinically suspected cases of those diseases specified under the Public Health (Infectious Disease) regulations 1988, and the revisions made in England in 2010. The revised measures are contained within the amended Public Health (Control of Disease) Act 1984 and its accompanying Regulations. These Regulations for clinical notifications came into force on 6 April 2010, and those relating to laboratory notifications on 1 October 2010.

• Notifiable zoonoses include anthrax and rabies.

Tuberculosis is also a notifiable disease. Clinical tuberculosis can result from infection with either Mycobacterium tuberculosis (which is not a zoonosis and is spread from person to person) or M. bovis (bovine tuberculosis).

Food poisoning is notifiable. Food poisoning has been defined as ‘any disease of an infectious or toxic nature caused or thought to be caused by the consumption of food or water’. Infections caused by zoonotic agents include the non-typhoidal salmonellas, campylobacter and cryptosporidium.

4. Enhanced surveillance

From time to time additional data are collected or specific surveillance studies set up, either nationally or locally, to provide information on certain aspects of a zoonotic infection.