69, 2^

Editorial

be reached. In some countries, however,the elimination prevalence at the subna-tional level will not be reached by 2005.

• All efforts to make MDT available free ofcharge to all leprosy patients should hesustained vigorously during the forth-coming years.

• Leprosy research—both basic and ap-plied—should he stimulated.

• Leprosy research requires substantial ef-forts for planning, organization, manage-ment, funding and coordination.

• The implementation of the eliminationstrategy under the auspices of the GlobalAlliance for Elimination of Leprosy re-

quires strengthened collaboration be-tween its various partners.

—Dr. Hubert Sansarricq

64160 Saint-Almon, France

—Dr. Denis Daumerie

Leprosy GroupStrategy Development and Monitoring

jar Eradication and EliminationDepartment a/ Control, Prevention

and EradicationWorld Health OlganizationGenera. Sit

Prevalence: a Valid Indicator for MonitoringLeprosy "Elimination"?

In 1991, the World Health Assemblystated that leprosy should be eli minated as apublic health problem by the year 2000(Resolution WHA44.9). Elimination wasthen defined as a prevalence rate below Icase per 10,000 inhabitants. Prevalence waschosen rather than case detection becausethe latter was considered as depending toomuch on operational factors. The assump-tion underlying the objective was that, sinceleprosy is an infectious disease directlytransmitted from the patients to the healthypopulation, a reduction of the prevalenceand. thus, of the reservoir would result in areduced transmission of the leprosy bacilli.This would lead, after' a number of years, toa decreased incidence of the disease. Sinceelimination was defined in terms of preva-lence, it seemed only logical to use that in-dicator to monitor the achievements of thestrategy. And indeed it was useful. Withmultidrug therapy (MDT), patients could bedeclared cured after a treatment of definedduration: this, accompanied by a systematicreview and cleaning of the leprosy regis-ters. resulted in a dramatic reduction in theregistered prevalence. From more than fivemillion cases registered in 1985, statisticshave gone down to less than $00,000 cases

in the year 2001. 1 This is undoubtedly agreat achievement: clinics are not congestedany more by large numbers of patients whono longer need any chemotherapy, andhealth workers can better concentrate on themore important issues of detecting andtreating the new cases and on preventingthe occurrence of disabilities.

In spite of its past usefulness. the preva-lence indicator clearly shows its limits now:

• Aker a dramatic decline, the decrease ofprevalence has been slow for the last 5years.

• Case detection did not decrease as ex-pected: It has indeed increased during thelast 4 years, even if a small decline hasbeen observed in the year 2000. The up-ward trends and the variations observedin the number of newly detected casescan easily be explained by a number ofoperational factors, such as the extensionof geographical coverage by MDT ser-vices and the intensification of detectionactivities through leprosy eliminationcampaigns (LECs) and other special ac-

' World Health Mg:wit:A:ion. Leprosy—glollal situ-ation. Wkly. Epiclinniol.1:cc. 75 (200(1) 226-23 I.

112^ International Journal of Leprosy^ 2001

tions. 13ut the fact is that after a numberof years of extensive MDT use, we donot consistently and convincingly ob-serve the expected decline in the numberof cases detected. Is it just a question ofwaiting for a few more years? Nobodyknows for sure. One could discuss atlength the assumption that a decrease inprevalence would automatically be fol-lowed by a decrease in incidence. At thetime of dapsone monotherapy, prevalenceand incidence were following the sametrend, and a decrease in incidence wasfollowed by a decrease in prevalence:prevalence decreased as a consequence ofthe decrease in incidence. This does notmean that a declining prevalence will au-tomatically result in a declining incidence.

At the time of diagnosis, leprosy pa-tients may already have infected all ormost of the people surrounding them: Itmay be that they are detected late: it mayalso he that some patients are infectiousbefore they develop any clinical sign ofthe disease. In any of these possibilities, ashortening of the infectious period afterdiagnosis (as is the case when patientsare treated with MDT compared to dap-sone) might have a very marginal effectonly.

An hypothesis which could in the pastbe considered as irrelevant is also regain-ing interest: patients may not be the onlysource of transmission.' The possible roleof healthy carriers or of environmentalsources of transmission is again ques-tioned.

• Prevalence is too much subject to artifi-cial changes devoid of any epidemiologi-cal meaning. The most obvious exampleresides in the consequences of the reducedduration of treatment. Clearly, a shift froma 24-month to a 12-month treatment formultibacillary (MB) leprosy, which re-duces the prevalence of MB leprosy by50%, has no influence at all on the risk oftransmission. With the single-dose rifam-pin-ofloxacin-minocycline (ROM) treat-ment, paucibacillary (PB) patients with asingle skin lesion do not even enter theprevalence any more, since they are con-sidered as cured on the spot.

=Lechat.^F. The source of infection: an unsolvedissue. Indian J. 1.epr. 72 (2000) 169-173.

• Prevalence does not reflect the actualworkload that the health services have toface. Many P13 patients detected during aspecific year do not appear in a pointprevalence, classically calculated at theend of the year: if they were detected inthe first half of the year, their treatmentmay be finished before the end of De-cember.

• In some countries, it is obvious that, evenwith a registered prevalence rate aroundor below I per MOM, leprosy remainsan important problem, either at the na-tional level because of gross underdetec-tion or in the provinces or states withincountries where the disease can remainhighly prevalent. In the Democratic Re-public of Congo, while the registeredprevalence rate was 1.04/10,000 at thenational level at the end of 1999, it was3.49 in the district of Tshuapa and 3.87 inthe district of Tanganika. 3

• With prevalence now more or less at thelevel of case detection, some countries(Bangladesh and Benin) are not consideredas endemic any more On the basis of theregistered prevalence, while their annualcase detection rate is above 1/10,000.'

• Registered prevalence can be very muchdifferent from the actual prevalence:

Coverage of the population by thehealth services is sometimes very poor.

In Madagascar, a LEC covering 2.27million inhabitants was carried out in1997. It led to the detection of 6810 lep-rosy patients, while only 1681 cases hadbeen diagnosed in the same districts dur-ing the preceding year.'

Another LEC implemented in sevendepartments in Niger detected 2228 cases,against only 472 in the previous year.'

Thus, the question is: "Is prevalence avalid indicator to monitor the leprosy situa-tion?- For me, the answer is clearly "No. Itdoes not measure (anymore?) what it is sup-posed to measure. - Since it is now confus-

'Bureau National de la Lepre. Progres versIT.Iim-ination de la Lepre (Rapport epidemiologique 1999).Repuhlitlue Democratique du Congo. Nlinistcre de laSante. 87 pp,

'world Ilcalth Orgiiiiiiittion. Leprosy eliminationcampaigns ( LECs)-progress during 1997-1998. Wkly.Epideiniol. Rec. 73 (1998) 177-182.

69, 2^ Editorial^ 113

ins and misleading. it would be better sim-ply to abandon it.

The situation we will have to face in thecoining years is completely different fromthat which existed in 1991. Prevalence hasgone down, and detection figures, with theirown limitations, appear from now on muchmore appropriate. We will now have to ver-ify the assumption that once the prevalencehas been reduced to a defined level, the dis-ease will disappear naturally.' Since the ul-timate goal of the elimination strategy is toreduce transmission, the relevancy of casedetection to monitor the success of the strat-egy is much higher than that of prevalence.Tuberculosis control programs do notbother collecting data on prevalence. Thereports they request deal with detection fig-ures and treatment outcome.' Do we needmuch more for leprosy'? As long as there re-main new cases to be detected in significantnumbers, leprosy remains an importantproblem. We all know that detection figuresare influenced by operational factors (but soare also, indirectly, the prevalence figures)and give only an approximate indication ofthe actual incidence. We all know that notall the newly detected cases are new cases:a proportion. or even sometimes a majorityof them, may have been ill for a number ofyears: they are the so-called "backlog"cases. but if they exist in significant num-bers, it means that leprosy services are stillfar from satisfactory. We all know that thenumber of patients detected increases if de-tection surveys are more frequent; someself-healing cases are then detected whowould not have been detected otherwise.That is why case-detection figures may not

`World Health Organiration. Guide to EliminateLeinmy as PlIbli(• Health Pmblem. 1st edn. Geneva:World Health Mg:it -Ili:16(m. 2000.

`Enarson. D. A., Rieder, H. L.. Arnadottir, R. andTrebucq, A. Itianagenient lithein I()SiS; a Guide torLow Income Countries. 5th edit. Paris: InternationalUnion Against Tuberculosis and Lung Disease, 20011.

be analyzed separately but in conjunctionwith other data. Knowledge of the activitiescarried out will be the first help to disentan-gle the interpretation problem. But other in-dicators will also be of invaluable assis-tance:

• Analysis of the trends in case detectionwill always be much more informativethan one-time data.

• The proportion of new cases with disabil-ities can give a rough idea about the de-lay before detection. In case of a stableproportion of new cases with disabilities,the trend in case detection can be consid-ered as reflecting with enough reliabilitythe actual trend in incidence.

• The proportion of children among thenew cases is an additional indicator:many children developing the disease un-doubtedly means active transmission.

Let us not forget one more thing: Leprosyis important because it is disabling. Themonitoring system used in any endemiccountry should thus also help us to analyzehow many patients still develop new dis-abilities in spite of the control program andhow successful we are in preventing dis-abilities.

I already hear the criticisms which willsay: "How will we classify the countries ashigh endemic or low endemic'!" I amtempted to answer with another question:"Do we really need to classify the countriesinto such groupsr Is it not a matter foreach country to decide what importance itwants to give to leprosy and its control, inview of the situation itself of course, butalso in view of the other health problems ithas to face, and the financial and technicalpossibilities to tackle them'?

—Etienne Declercq, M.D.Damien Foundation13oulercd Leopold IL 2631081 Bru.s .sels, Belgium