9.1.1. Understanding the concept of surveillance

Surveillance is the collection, collation and analysis of health data that enables the prompt dissemination of the information to those who need to know, in order that appropriate action may be taken. Effective surveillance is essential to any prevention and control programme and encompasses the mechanisms for disease detection, confirmation of diagnosis, reporting, collation of data and reporting back of the data to the source. Detection of rare diseases requires well-trained veterinary or human health-care providers. Confirmation of reports of suspicious cases requires appropriate laboratory support. Reporting requires mechanisms for easy communication of cases, and also some incentives for reporting or disincentives for not reporting. Many countries rely on disincentives for not reporting diseases under surveillance (reportable diseases). Regulations exist for reporting certain diseases (usually of high epidemic potential or with high morbidity or mortality rates) in most countries of the world.

Because of its epidemic potential, associated high morbidity and mortality rates, wide-ranging occurrence, and history of threatened use – and now actual use in the 2001 anthrax letter events – as a biological terrorist weapon, anthrax in humans or animals should be included on all national notifiable-disease lists.

Surveillance systems vary widely in objectives and methodology. The surveillance scheme outlined below may be adapted to accommodate the local veterinary and public health systems within a country. It should be noted that efforts to improve certain attributes of surveillance, such as specificity, may detract from other attributes such as timeliness.

9.1.2. Intersectoral cooperation

As with most zoonotic diseases where animals serve as the primary sources of human infection and epidemics (as opposed to zoonoses, where both humans and animals may be infected from common environmental sources), control of anthrax among humans depends on the integration of veterinary and human health surveillance and control programmes. Routine cross-notification between the veterinary and human health surveillance systems should be part of any zoonotic disease prevention and control programme, and close collaboration between the two sectors is particularly important during epidemiological and outbreak investigations.

High-risk areas for human disease may be identified pre-emptively by review of veterinary surveillance information by veterinary or public health authorities. Because herbivorous livestock and wild animals are more susceptible to B. anthracis than humans, and because in general soil sources do not represent a threat to humans directly, the potential threat to human populations is through contaminated animal products. The exceptions to this rule are biological warfare or terrorism, or laboratory settings where the spores of B. anthracis may be manipulated and concentrated in an unnatural way to represent a direct threat to human health through respiratory, gastrointestinal or cutaneous exposure – see also section 4.2.3. However, many countries rely on detection of human disease as the alert of anthrax epizootic activity. In these cases, humans may be considered sentinels (see also section 4.1). Ideally, this should not be the case, and enzootic and epizootic surveillance and reporting should lead to the implementation of anthrax control strategies that prevent human cases altogether. Realistically however, in many countries the support and infrastructure for human health surveillance programmes is greater than for veterinary equivalents. In such cases, when detection depends on the appearance of a human case, the control of anthrax among livestock is delayed and the losses suffered by farmers will be greater than if a functional veterinary surveillance programme is in place. This is because only a fraction of the livestock cases are ever identified and the disease goes unreported and uncontrolled.

9.3.1. Local level

Animal and human health-care professionals, with their supporting laboratories, form the front line of any zoonotic disease surveillance system. Surveillance begins with the first point of contact by a veterinarian or clinician in the event of a suspicious case. In an optimal situation, concern over a suspicious case should result in either contact with local health authorities (veterinary or human) or the initiation of a case-reporting form.

Depending on the objectives of the surveillance system, a case form should be completed on every suspected or confirmed case. Depending on veterinary or public health resources, this case-report form may be completed by the local health-care professionals attending the suspicious case, or preferably by health authorities at the local level (municipal or county).

Figs 11&12 are examples of human and veterinary case-report forms. Minimum data elements for human case-reporting are:

Fig. 11

Sample anthrax case-report form (human).

Fig. 12

Sample anthrax case-report form (animal).

• case classification (e.g. suspected or confirmed);
• clinical form of the case (cutaneous, gastrointestinal, inhalational, meningeal);
• identifying information, and a unique identification code.

Depending on the objectives of the surveillance system, other pertinent data might include age, sex, geographical information, occupation, date of presentation, exposure history, nationality, date of clinical onset, treatment and outcome.

The local level (health-care centre, private clinic and physician, and other health personnel) is the first point of official contact with the infected patient and the point at which surveillance data should first be collected. Suspected rather than confirmed cases may be reported from this level to higher levels. The tasks at this level are diagnosis and case management, including treatment and health education plus, resources permitting, case and outbreak investigation. The laboratory criteria for the confirmation of any suspicious case may be included on the same case-report form, or the form may be simplified to only include whether the case was confirmed or not. Local health authorities may be asked to assist in diagnosis and case management.

Local health authorities are responsible for reporting to the intermediate level (i.e. state) or to the central level (i.e. federal), depending on the government structure. Also, local health authorities will be expected to mount the early epidemiological investigation targeted at:

• identifying and controlling the source of infection (including additional case-finding, case-confirmation, identification of source of infection and tracing sources of infection from infected animals or animal products);
• reducing population morbidity and mortality through initiation of control measures depending on the authority, epidemiological situation and guidelines.

Control measures for anthrax in livestock are given in chapter 8 and Annex 4. Depending on the epidemiological details of any human outbreak, control measures for humans are based on removal of the source of infection from human contact or separation of human populations from the infectious source(s); however, these control measures may vary widely in detail and will depend on the particular exposure situation.

9.3.2. Intermediate level

Depending on the political infrastructure, data from the report forms may be managed at an intermediate level such as a state health or veterinary department. Here the data may be collated and analysed for feedback to the local (municipal or county) level. Usually, the intermediate level collates and analyses data from local levels. In addition, personnel at this intermediate level may serve as support to the local level. The tasks of the intermediate level are:

• aspects of case-confirmation and case-management that cannot be undertaken at the local level;
• analysis of data from local levels;
• epidemiological investigations, tracing sources of infection from infected animals or animal products;
• initiation and monitoring of control measures.

9.3.3. Central level

Reporting of cases should also be transmitted to the central level. Depending on national resources, the central level will analyse and report the data back to the intermediate and local levels. In addition, the central level may formulate national policies and allocate resources based on the surveillance information. The central level may also provide technical support (e.g. laboratory or epidemiological) to the intermediate and local levels as appropriate, and it is responsible for reporting summary surveillance information to international authorities such as WHO and OIE.

9.4.1. Case definition

Details of the clinical presentation of anthrax in humans can be found in chapter 4.

The suggested case definitions below may need to be adapted to local needs and laboratory capabilities available for confirmation of diagnosis (WHO, 1997b).

9.4.2. Case classification

9.4.3. Special considerations for human surveillance

A single case of anthrax in a human population should result in a report and investigation.

Because the disease is rare in many countries, continuing education programmes for health-care providers should include information on recognition and confirmation of this disease.

Certain at-risk populations may warrant active surveillance (the implementation of case-finding activities among a subpopulation) on a regular basis. One example of such a need was found among hair and wool industry workers in Europe and the United States in the 20th century. Because of an especially high risk, these workers were more intensively observed for anthrax than the general population by the occupational health systems and authorities serving these groups.

9.5.1. Case definitions

9.5.2. Case classification

9.5.3. Special considerations for veterinary surveillance

• In countries or areas free of anthrax, the disease is treated as an exotic or foreign disease, and measures to be adopted are based on primary prevention, mainly the control of imported animals and animal products (see Annex 4).
• In enzootic countries or areas, whether or not animal vaccination is carried out, all suspected sudden deaths in animals should be investigated as possible cases of anthrax. Flocks or herds in direct or indirect contact with positive human cases should be investigated, as the human infection will have derived from animal cases and any infected herds or flocks should be identified and vaccinated. The primary prevention measures mentioned above should also be in place. In enzootic countries or areas where animal vaccination has been discontinued, particular emphasis should be placed on continued surveillance.
• Because the numbers of animals may be very large on individual affected properties, the unit of reporting may in some cases be the property or farm rather than the animal.
• Whenever possible, global positioning data should be included in case-reporting to ensure that affected areas are properly located and recorded.

In general, the occurrence and reporting of anthrax may cause economic harm to affected animal producers. For that reason, it is important that national programmes for anthrax control include no penalties for reporting and compensation for additional costs to the farmer. Anything that discourages reporting should be avoided, and everything that encourages reporting should be embraced. Suggested approaches to ensuring this are:

• Compensation to the owner should be available for any carcass proven (i) to be a case of anthrax, and (ii) to have been incinerated or disposed of by another officially approved method. Ideally, disposal of the carcass should be carried out by the official veterinary service.
• The initial vaccination of the herd or flock should be carried out by the official veterinary service.
• Quarantine should be kept as non-onerous as possible; it need not be longer than 21 days after vaccination of the affected herd has been carried out (see section 7.2.1.2); or, if cases continue to occur after vaccination, 20 days after the last case, according to the OIE-designated period (Annex 4).
• Animal health officers should be properly equipped with specimen-collection materials, equipment and materials necessary for disinfection, cleanup and disposal, and with antibiotics and vaccine plus syringes and needles. They should also be appropriately trained (e.g. not to administer vaccine and antibiotics simultaneously – see section 7.2.1.3) and, furthermore, should have the necessary transport and suitable office support for reporting cases.
• The laboratory technician should be supplied with the appropriate equipment, materials and training for confirmation of diagnosis.
• Appropriate educational literature for all persons involved, from the farmer/owner to ministry levels, and information packets for the media should be produced.
• Every effort should be made to get local understanding and popular support for the policy of carcass destruction and herd vaccination.
• The reporting system should be based more on incentives than penalties, although penalties for failure to report may be necessary. The reporting should not incur cost (e.g. forms, postage, etc.) to those required to make reports.
• Treatment and vaccination of the remainder of the herd/flock and the services of the animal health officers in assisting with cleaning and disinfection should be free of charge.
• Affected herds/flocks should be revaccinated annually for three years (sections 8.8, 8.9).