Estimated number of leprosy cases in the world.

Planning for disease control requires estimates of the number of leprosy patients from local to global levels. From the mid-sixties to the mid-eighties, global estimates appeared to be constant at between 10 and 12 million. The introduction of multidrug therapy (MDT) in many countries and the consequent reduction of prevalence of the disease has necessitated a reassessment of the global estimate. Based on available information and its interpretation, the number of leprosy cases in the world in 1991 has been estimated at 5.5 million. The number of individuals with deformities due to leprosy, including persons now cured of the disease, has been estimated at between two and three million.

Estimated number of leprosy cases in the world.

Planning for leprosy control requires estimates of the number of leprosy patients at different levels. During the period between the mid-1960s and the mid-1980s, global estimates had remained constant at between 10 and 12 million. The introduction of multidrug therapy (MDT) in many countries and the consequent reduction of the disease's prevalence has necessitated a reassessment of this. Based on available information and its interpretation, the number of leprosy cases in the world for 1991 has been estimated at 5.5 million. The number of individuals deformed by leprosy, including those cured of the disease, has been estimated at between 2 and 3 million.

Issues involved in the rapid assessment of the leprosy problem.

Sample surveys for estimation can prove very expensive and time-consuming because of the enormous sample sizes usually required. Where sample surveys have to be undertaken, diagnoses should be limited to detecting a case of leprosy, without attempting skin smears etc. in order to classify by types. Usually enough knowledge is available on the approximate proportion of multibacillary (MB) cases in most communities, and this knowledge could be utilized for estimating the caseload by types of leprosy. Again intensive tracing of nonrespondents could be limited to either males or females depending on convenience, and well-known sex ratios among patients utilized for deriving estimates for the other sex. The type of rapid methods of estimation depend on three types of situations: (1) before multidrug therapy (MDT); (2) 5 years or more after MDT; and (3) less than 5 years after MDT. In the first situation one or more of the following methods are suggested: (i) extrapolation from registered cases; (ii) extrapolation from child prevalence; and (iii) conducting rapid village surveys. In situations where MDT has been introduced for 5 years or more the registered cases plus a small number, depending on local experience, would seem to be adequate. When MDT was introduced less than 5 years before, it is suggested that the prevalence rates be obtained by statistical interpolation drawing on the experience from areas which have had more than 5 years of MDT.

Estimated number of leprosy cases in the world.

Planning for disease control requires estimates of the number of leprosy patients from local to global levels. From the mid-sixties to the mid-eighties, global estimates appeared to be constant at between 10 and 12 million. The introduction of multidrug therapy (MDT) in many countries and the consequent reduction of prevalence of the disease has necessitated a reassessment of the global estimate. Based on available information and its interpretation, the number of leprosy cases in the world in 1991 has been estimated at 5.5 million. The number of individuals with deformities due to leprosy, including persons now cured of the disease, has been estimated at between 2 and 3 million.

PIP: World leprosy estimates are discussed and generated for 1991. In an effort to identify 5.5 million registered leprosy cases in the world for 1991 it was found that there also are 2-3 million people with deformities due to leprosy. The rehabilitative requirements of this population need to be served in addition to the continued multidrug therapy (MDT) needed to control prevalence. Successful leprosy control has led to a reduction from prior estimates of 10-12 million cases. There are many problems in estimating because of the low frequency of occurrence and its uneven distribution. Well-planned sample surveys are practical and cost effective only in limited areas, rather than for countries as a whole, and also include nonsampling errors. Multimethods were used to derive the world estimates, and the estimates have been adequate for planning purposes. The magnitude of the problem was addressed in 1966 by the WHO which reported 10,786,000 cases which remained stable through 1972. A 1983 estimate by the WHO Study Group on Epidemiology of Leprosy in Relation to Control was 11,525,000 cases. 95% of registered cases are from 25 countries, of which 5 countries contribute 82% (Nigeria, Brazil, Myanmar, Indonesia, and Bangladesh). The current estimates focused on these countries. In the 5 countries, not only were correction factors applied to registered cases, but intensive reviews of all available information and discussions with relevant program managers were conducted. Correction factors for each region were used unless more reliable information was available. The correction factor was calculated as the ratio of registered cases in the top 25 countries in the region to earlier country estimates. There were 5 reasons why estimates in 1991 were significantly lower: 1) cases cured through MDT, 2) removal of cases not fitting the WHO definition which requires a case to be someone receiving MDT treatment or needing treatment, 3) late effects of an intensive dapsone-based control effort, 4) strengthened control activities, and 5) natural declining trends. The patients needing rehabilitation were estimated by considering the past case records over 50 years and the proportion with deformities, the survival rate of those deformed, and the nature of control activity. Estimates and registration of cases is given for 25 countries.

Control of trachoma and prevention of blindness in rural communities in Burma.

Trachoma was identified as the single most important cause of blindness in central Burma in a study carried out in 1961-1962. Control measures started in 1964 considerably reduced the degree of endemicity and severity of the disease in the areas treated. According to recent simplified criteria of evaluation, the prevalence of active trachoma has been reduced by more than 60% and that of active inflammatory disease of moderate and severe intensity from 7.4% to 1.8% of the active cases. A reduction in the risk of becoming infected is evident from changes that have occurred among the younger age groups.The experience acquired by the trachoma control project in central Burma-covering a population of more than 4 million in 8000 villages-emphasizes the importance of the active participation of the community and the role of local auxiliary personnel. Most of the activities, including surgical repair of trichiasis, are the responsibility of health assistants; their training includes, in addition to the recognition and treatment of patients requiring topical application of antibiotics or surgical repair of trichiasis, the screening and referral to the general practitioner or to the eye specialist of those needing more specialized attention.The results already obtained have made possible a gradual replacement of control activities by a surveillance programme, and their integration into the basic health services. The objectives of the trachoma control programme have been expanded to include the prevention and management of other causes of preventable or curable blindness, with special emphasis on eye injuries and glaucoma.

The use of simple epidemiological models in the evaluation of disease control programmes: a case study of trachoma.

One of the problems in the quantitative evaluation of disease control programmes is the definition of a "critical" index reflecting the effect of control measures on the various aspects of a polymorphic disease. Trachoma is an example of a polymorphic disease in which its activity, intensity, severity, etc., are affected by control measures, including their timing. A simple epidemiological model indicated that the "force of infection" is a sufficient parameter to describe changes in the disease picture following a control programme. Use was made of two trachoma prevalence sample surveys in the same communities, one carried out in 1960-61 and the other in 1968-69. Total trachoma age-prevalence histograms were constructed and simple catalytic curves fitted with the help of a computer programme developed for this purpose. A reduction in the force of infection in the cohort born after the institution of control measures was found. Its projection to the whole community indicated that the control programme had reduced the disease load to 20.1%, i.e., about two-fifths of its former level.

Use of excess mortality from respiratory diseases in the study of influenza.

Since 1970, WHO has conducted a collaborative study on the use of "excess mortality" from respiratory diseases (that is, the number of deaths actually recorded in excess of the number expected on the basis of past seasonal experience) in order to assess in 13 different countries the severity of influenza epidemics. The use of computer-produced seasonal expected and actual curves permits quick visual assessment of influenza activity in any one country, as well as comparisons between different countries. The study demonstrates that an excess in the observed over the expected number of total deaths does not necessarily indicate an excess in deaths from influenza, and it is therefore limited, at least for the present time, to deaths from respiratory disease. It provides a week-to-week record of deaths from acute respiratory disease in countries where weekly returns are available and a retrospective analysis of the disease pattern in the collaborating countries. This study will be continued for a number of years and, apart from its value to the individual countries, should provide useful comparisons between countries with different climates.

Collaborative assay of a proposed international standard for tetanus toxoid (adsorbed).

An international collaborative assay was performed with the aim of establishing an international standard for tetanus toxoid (adsorbed). Six laboratories participated. A suitable preparation in the lyophilized state was made available by the Paul Ehrlich Institut, Frankfurt am Main, Federal Republic of Germany. Preliminary experiments showed that there were no significant differences between individual ampoules and that the preparation was highly thermostable.The proposed preparation (A) was compared in guinea-pigs and mice with the existing international standard for tetanus toxoid (B), which is a plain toxoid, with another arbitrarily chosen adsorbed toxoid (C), and with a number of locally prepared preparations (D). In the mouse tests preparation B was omitted. It was found in the guinea-pig tests that 1 mg of the proposed standard contained an activity equivalent to 1.5 IU if compared with the non-adsorbed international standard but since the slopes of the log dose-response lines for the adsorbed and plain types of preparation were not parallel, this is a rough approximation only. When the different adsorbed preparations were compared, there was close correlation between the guinea-pig tests and the mouse tests. In the guinea-pig test 1 ml of preparation C corresponded to 126.5 mg of preparation A and in the mouse test to 129.9 mg of preparation A. In one laboratory comparative tests were made by titrating blood antitoxins after immunization of guinea-pigs with graded doses of the toxoids. The results corresponded very well with the data from challenge tests (1 mg of preparation A contained 1.5 IU of the plain toxoid in challenge tests and|1.4 IU in the titration test).Preparation A was established by the WHO Expert Committee on Biological Standardization as the international standard for tetanus toxoid (adsorbed) and the international unit was defined as the activity contained in 0.6667 mg of the international standard.

International collaborative studies on potency assays of diphtheria and tetanus toxoids.

Collaborative studies showed that relative potency assays for a particular type of diphtheria toxoid (adsorbed) and for tetanus toxoid (plain and adsorbed) gave very similar results, whether the assays were carried out by toxin challenge or by antitoxin titration after immunization of experimental animals with graded doses of toxoid. The same numerical results were obtained with a scoring system as with a system based on survivals only. Although skin tests were used on a very limited scale in these studies, it seems likely that they could replace lethal tests for the diphtheria challenge assays.For both tetanus and diphtheria, the adsorbed toxoid gave a higher relative potency when combined with other antigens than as a single toxoid. Both mice and guinea-pigs were used for the lethal challenge test of adsorbed tetanus toxoid. For the single tetanus toxoid the results were the same, but for the combined toxoid (DPT vaccine) the mouse assay results were about twice those of guinea-pig assays.