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Virtually every country intheworldhasaNationalTuberculosis Programme (NTP) that takes primary responsi-bilityfortuberculosis(TB)control.TohelptheNTPsachieveeffective worldwide TB control, the World Health Assemblyapproved two targets in 1991: to cure 85% of detected newcases of sputum smear-positive TB, and to detect 70% ofexisting cases of sputum smear-positive TB. The appropriate-ness of these targets has subsequently been confirmed usingcomputer modelling. The targets are based on two observa-tions: cases that receive inadequate treatment are likely tosurvive for many years while remaining chronic transmitters,and untreated smear-positive patients are expected to remaininfectiousforapproximatelytwoyearsafterdiseaseonset,thendie or recover. On average they cause one additional infectivecase within these two years. In areas with no TB controlservices, an equal number of people die of TB and becometransmitters — that is to say, the number of TB transmittersneither increases nor decreases over time.The World Health Organization (WHO) emphasizesthe need to attain the cure rate target first, as high numbers offailed treatments can actually lead to an increase in TBincidence due to the creation of chronic transmitters (asmentioned above). Only when the first target has been metshould case-finding be increased until the second target ismet. The case-finding target was set at 70% as being thehighest level that could reasonably be attained in averagedeveloping country settings. The higher the case-finding rate,the faster incidence will fall.A keystone of TB control has always been that activecase-finding is unnecessary as TB symptoms are sufficientlyseverethatcaseswillseektreatment(whenitisavailable)soonafter they develop TB. In the past, virtually the only TBtreatment available in developing countries was provided bygovernment health services. Therefore, when setting targetsfor TB control it was assumed (although not explicitly) thatother providers such as private practitioners, traditionalhealers, etc, could be neglected. It was assumed that themajority of cases not treated by government health serviceswould die — leaving few to become chronic transmitters.Thatwasbeforetheexplosioninthenumbersofprivatepractitioners in Asia and other areas of the developing world,however. Nowadays, cases that are unknown to the NTP donot die after two years. Instead they seek treatment fromprivatepractitioners,anditiswidelyagreedthatthistreatmentis normally of very poor quality with very low cure rates. Themajorityofpatientswhoreceivepoortreatmentneitherdienorare cured of the disease, but remain sputum-positive andchronictransmittersofTB.Thetime-spanbeforetheyceasetobechronictransmitters(becausetheydie,ortheirinfectivenessbecomesnegligibleortheyobtainatruecurefromtheNTP)isunknown, but experiencehas shown that substantial numbersof patients seek treatment from NTPs months or even yearsafter first seeking treatment from other providers.We can estimate the effects of private practitioners bycomparingthepercentageofcasesinsettingswithandwithoutprivate practitioners who may become chronic transmitters.First, consider a programme just meeting both targets, in asetting wherethe number ofprivate practitionersis negligible.Ofevery100peoplewhodevelopsputum smear-positiveTB,70 will be detected and 30 will either die or spontaneouslyrecover. Of the 70 who are detected, 85% will be cured, but15% will not, and could potentially become chronictransmitters. Thus, of our original 100 patients, 11 at most(15% of the 70 detected) could become chronic transmitters.Realistically, unless they receive further treatment, a highproportionofthese11willdieduringoraftertreatment.Ifweassume, for argument’s sake, that only 40% of these potentialchronic transmitters actually become chronic transmitters, wewouldexpectatmost4ofouroriginal100patientstobecomechronic transmitters.Underthesesameconditions,aprogrammejustmeetingboth targets in an area with a high number of privatepractitioners could again expect less than 4% of all cases tobecome chronic transmitters following NTP treatment.However, the cases treated by private practitioners outsidetheNTP(30%ofallcases)couldbecomechronictransmitters— giving a total of 34%.The above calculations imply that poor cure rates byprivate practitioners may lead to a transmission rate more thaneight times that which is ‘‘just acceptable’’ for effective TBcontrol within NTP programmes. The calculations are approx-imate because detailed data on ‘‘average’’ private practitioners’cureratesarenotknown(giventhenatureofprivatepracticesindeveloping countries, these probably never will be directlyavailable), and because of the added complications of TBsufferers seeking care from a succession of providers. Even inthehighlyunlikelyeventthatprivatepractitionerscurrentlycureas many as 50% of their TB patients and only 30% of theremainder become chronic transmitters, the number of chronictransmitters resulting from private practitioners will more thanmatch those resulting from NTP treatment. Of course in Asiaand other settings, the situation will be worse, as the percentageof TB patients seen by private practitioners is much higher than30%.The figure often quoted is 60%.

The implications for TB control of the growth in numbers of private practitioners in developing countries.