| Opportunities for Control of Dracunculiasis (1982) |
Baseline epidemiologic and water use information is required to plan control programs, to determine the time of the year when educational activities and water treatment will be most effective, and to assist in selecting sites for installation of protected water supplies. Although data collection and surveillance are discussed here solely in terms of dracunculiasis, the methods outlined could certainly be incorporated into existing disease control or surveillance activities or could be used to assess the extent of other water-related health problems. Public health authorities in countries where dracunculiasis occurs will want to assess the extent of the problem at the national level before initiating control activities or surveillance. This section is intended to (1) establish guidelines and definitions for data collection and analysis relevant to dracunculiasis, (2) to suggest practical approaches for conducting an initial assessment of the dracunculiasis problem at the national level, and (3) for those districts or villages where dracunculiasis is occurring, to describe various methods of collecting epidemiologic information about cases and organizing these activities into a surveillance system.
Despite the relative simplicity of the life cycle and epidemiology of Dracunculus medinensis, some traditional terms need to be defined more precisely to promote communication and enhance the comparability of data over time and among different areas. The definitions that follow are based on current parasitologic and epidemiologic knowledge of the disease. As future research and experience adds to the understanding of dracunculiasis, these definitions may need revision. (Names and parts of the definitions in brackets indicate synonyms or optional inclusions.)
A person in whom an investigator, health worker, or other trained person sees the Dracunculus medinensis worm beneath or extending from the skin. Also, a person with an acute skin lesion from which the larvae of D. medinensis have been identified by a trained person using microscopy or other means.
[Retrospective or historical case] A person who reports having experienced the emergence of one or more D. medinensis worms within the past 2 years.
A person who has been infected with dracunculiasis or who has ingested infective larvae but who has not yet manifested clinical symptoms or signs of the disease such as blistering, ulceration, and worm emergence. There is no specific diagnostic test to identify such cases at present.
A local administrative or social unit (e.g., village, hamlet, town, city) in which indigenous active or presumptive cases of dracunculiasis, or both, have been reported during the previous 2 years.
The period of time between ingestion of infective D. medinensis larvae by a person and the onset of clinical symptoms.
Peak patency period
[French: period de mise en evidence communitaire] Period of the year during which more than 50 percent of all eases (in a community or defined geographic area) are reported. This definition applies to areas where incidence is seasonal.
Individual patency period
[French: period de mise en evidence individual] The interval in an individual case between the time of first parasitologic evidence of the worm beneath or extending from the skin (or onset of typical skin blister from which a worm will soon emerge) and the time of complete expulsion or extraction of the worm from the body.
Unprotected water source
Source of drinking water that contains Cyclops and that either allows partial or total immersion of an infected person in the water source or permits water runoff to enter. Such sources are also likely to contain unacceptable levels of microbiological contaminants.
Protected water source
Source of drinking water that prohibits the partial or total immersion of an active guinea worm case and contamination from ground runoff. Such sources are usually constructed so as to remain free from fecal pollution.
Infested water source
Source of drinking water containing Cyclops species capable of ingesting first-stage larvae (L1) of D. medinensis.
Infective water source
Source of drinking water containing Cyclops infected with third-stage larvae (L3) of D. medinensis.
The continuing collection, analysis, and feedback of epidemiologic data based on reporting or detection of cases of disease.
Passive case reporting
Recording of cases that voluntarily come to the attention of public health authorities. Passive reporting or surveillance is achieved through the establishment of routine reporting mechanisms and is useful for obtaining initial data on the distribution of dracunculiasis in an area.
Active case detection
Search for cases by representatives of the health system through a village-to-village or house-to-house survey or a sample of the population thought to be at risk. This method usually reveals more cases than does passive reporting.
The rate of appearance of new cases in a defined population within a specified period of time, usually 1 year.
The proportion of a given population showing patent dracunculiasis infection at a given point in time. Prevalence data may be of little use with regard to dracunculiasis because the period of patency is usually short and seasonal. Therefore, information collected during low transmission periods can be misleading. Prevalence should be measured at the period of peak patency.
Reduction of disease incidence in a defined area over a period of 24 months through planned activities.
Complete absence of new indigenous cases of patent dracunculiasis infection in a previously defined endemic area for a period of at least 24 months given the presence of an active surveillance system, including at least two annual village-to-village checks.
Global elimination of human dracunculiasis infection.
Public health authorities in countries with reported cases of dracunculiasis should be able to identify endemic regions, provinces, and some affected communities using existing information. Although data from secondary sources may reflect less than 10 percent of actual cases, they indicate the approximate areas of endemicity, geographic distribution, and peak transmission seasons for dracunculiasis. Possible sources of information regarding incidence and distribution of dracunculiasis within a given country include:
- Communicable disease surveillance records for preceding 20 years
- National communicable disease specialists
- National medical and scientific literature
- International medical literature (write to International Health Program Office, U.S. Centers for Disease Control, Atlanta, Georgia, 30333, USA)
- Meteorologic records for preceding 20 years
- Water and sanitation records from communities with protected or potentially infective water sources
- Mass media (print)
- Hospital and outpatient clinic records.
Information from secondary sources can be supplemented by responses to questionnaires prepared by national public health authorities responsible for communicable disease control and sent to state and district health officials (World Health Organization 1983). Information that can be derived from questionnaire responses might include:
-Number, name, and location of villages with new cases of dracunculiasis within the preceding 24-month period
- Peak transmission season for dracunculiasis
- Estimated annual incidence of dracunculiasis (i.e., new cases in an estimated residential population)
- Names of health workers or physicians in affected villages.
Relevant portions of the questionnaire should be filled out by or in consultation with the official in charge of water and sanitation for that state or district. Better response rates will be obtained if the questionnaire is announced and discussed at a health officers' meeting or is followed up shortly with telephone calls or personal visits. The questionnaire might best be distributed in the month following the suspected peak transmission season. A sample questionnaire and cover letter used by the National Institute of Communicable Diseases in India appear in Figure 8.
This initial assessment will allow national health authorities to determine if and where dracunculiasis is endemic, to identify geographic areas requiring more aggressive data collection, and to determine an appropriate course of action (see Table 2).
Countries in which a dracunculiasis control program is being planned or has already been started at the regional or national level should establish a surveillance system. The main objectives of a dracunculiasis surveillance system should be to identify affected villages and to determine the number of people affected by the disease. A surveillance system can be either passive or active. The type of system selected should depend on (1) available resources, (2) estimated extent of the disease, and (3) existing mechanisms for case reporting.
Passive surveillance uses existing reports of disease from health authorities, published and unpublished studies, and other data already available from local, national, and international sources. Medical authorities may be queried by questionnaire. The major disadvantage of a passive surveillance system is that an overwhelming majority of the cases will not be reported. In a study conducted in Togo in 1977, less than 4 percent of dracunculiasis cases had been reported. Another study in Rajasthan, India, in 1978-1979, found that none of the 985 patients identified as active cases in the study had visited a health center (Johnson and Joshi 1982). Careful study of passive surveillance data can provide a basis for tentative judgments about which regions in a country are affected and which of those are likely to be most heavily affected. If a serious effort to control or eliminate the disease is planned or contemplated, however, some form of active surveillance will be required.
TABLE 2 Possible Courses of Action Based on National Problem Assessment
Information from National
Dracunculiasis reported to have occurred in only several areas more than 2 years ago
Continue to review passive case reports and search actively for cases in small sample of villages within suspected areas.
Dracunculiasis reported in several contiguous provinces
Initiate regional surveillance and control activities.
Dracunculiasis reported from provinces representing 50 percent or more of national territory
Initiate national surveillance and begin control activities in known affected areas.
Active surveillance methods are employed to seek information about affected individuals and villages that is not reported. Aggressively applied, such a system can detect virtually every affected village and patent case. It does, however, require mobilization of numerous health and other workers and volunteers, rigorous supervision to ensure reliable results, and high investments of time and money. Techniques include stimulation of the routine reporting system by means of an information campaign to increase reporting of the disease by medical authorities and by the public; use of "sentinel" sites such as schools, markets, and selected outpatient departments of clinics to inquire about cases in their catchment areas; and an active village-to-village or house-to-house search for cases.
Recognition cards or color photographs of patients with typical signs of dracunculiasis infection might be used to enhance diagnostic accuracy in areas where the disease is newly introduced or occurs infrequently. This technique was used in the successful smallpox eradication program. Dracunculiasis, however, is more distinct than smallpox and is well recognized by most villagers in highly endemic areas, so the value of such recognition cards--as indicators of an "official" inquiry or as true aids to diagnosis where the disease is not well known--remains to be determined.
To ensure comparable and consistent reporting, investigators should distinguish between an active dracunculiasis case (one in which the investigator or other trained inquirer actually sees the adult guinea worm beneath or extending from the skin), and a presumptive case (in which the past emergence of a worm is reported, with compatible scar(s) or ulcer(s)).
Active searches for cases have recently been employed quite effectively in the Indian Guinea Worm Eradication Program. A questionnaire circulated to responsible health officers in that country in October 1979 (see Figure 8) yielded reports of 1.8 million people in 728 villages at risk of the disease; however, active searches conducted in January-February 1981, and in September-October 1981, revealed 5.9 million persons in 7,533 villages, and 12.2 million persons in 10,582 villages to be at risk, respectively. Thus it is likely that an apparent increase in cases will follow an active search for cases.
The surveillance system should collect no more detailed information than the control efforts require at each stage in the program. In some situations it may be sufficient simply to identify the villages where dracunculiasis occurs, without regard to the number of cases. In other situations, and especially as incidence of the disease reaches "low levels, it will be necessary to enumerate all affected patients and eventually to identify every case by name.
Collection Of Baseline Information
Before initiation of control activities, responsible public health authorities should collect baseline information from households in a small representative sample of villages during the peak transmission season. These data are essential for subsequent evaluation of a control program. A household sample survey might include the following categories of data:
- inspection Basic epidemiologic indicators (e.g., incidence rates, geographic distribution, size of population, and age groups affected) must be established for endemic districts and communities through active inquiries.
- The location, type, and use of infective water sources must be determined through visits to affected communities and inspection of suspected sites.
- Health beliefs, knowledge, and practices regarding dracunculiasis and water used for drinking must be ascertained for each identifiable ethnic or cultural group affected, including village leaders and women and children.
A sample household survey questionnaire that incorporates some aspects of each of these information categories is shown in Figure 9. At a minimum, a reasonably reliable estimate of the annual incidence of dracunculiasis and the size of the population at risk or number of affected villages, or both, should be obtained before control measures are undertaken, to provide a basis for comparison later.
Recommended and optional data that should be collected as part of surveillance and control activities are outlined in Table 3.
More detailed baseline data can be obtained by conducting special studies in affected communities. University students might be enlisted to conduct observational studies, collect water samples, and prepare maps and charts of sources of drinking water. These special studies should be planned and coordinated with other data-gathering activities. Possible topics for such studies are shown in Table 4.
Other activities that may be initiated as part of surveillance include:
- Development of a practical field manual(s) for programs of surveillance, control, and elimination of D. medinensis, for example, the India program manual (National Institute of Communicable Diseases 1982)
- Development and evaluation of training materials and methods for carrying out control programs.
TABLE 4 Topics and Methodology for Conduct of Special Studies
Sampling of water sources for identi fication and quantification of cyclops populations and D. medinensis larvae
Water-use practices related to dracunculiasis
Observations of water collection, bathing, laundering, swimming, wading, etc.
Knowledge of disability, prevention, and treatment of dracunculiasis and attitudes toward the disease
Household interview survey of all households--or a representative sample of households--in a community
Impact on economic production
Surveys of agriculture, employment, cooperatives, or production
Impact on school attendance
Review of attendance records at local school(s)