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Year : 1991  |  Volume : 57  |  Issue : 1  |  Page : 22-24

Use of modified Ridley's bacteriological scale for assessment of multibacillary leprosy cases under multidrug therapy

Correspondence Address:
S S Naik

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In order to obtain proper judgement of bacterial quantum in human source (leprosy cases) a modification to Ridley's Bacteriological Index is suggested by applying formula as follows : Average Bacteriological Index of the group of patients X No. of patients in group X "scoring point" based on Ridley`s logarithmic Bacteriological Index scale.This new system based on arithmetic scale has been applied to multibacillary leprosy cases under multidrug therapy in leprosy colonies and leprosy control unit in an urban area. This comparison revealed that the introduction of multidrug therapy initiated a reduction in total bacteriological quantum very fast (i.e.) 100% to 5% at 12 months, 2.5% at 24 months in leprosy colonies where there was no entry of multibacillary case. However, in the urban slum there is an influx of new multibacillary cases every year, though bacterial quantum reduced as compared to initial status, it has remained static even at 60th month. The application of modified Ridley's Bacteriological scale to judge "total bacterial quantum : in any given control area gives a more realistic indication of the progress of MDT programme.

Keywords: Bacteriological quantum, Multidrug therapy (MDT)

How to cite this article:
Naik S S, Ganapati R. Use of modified Ridley's bacteriological scale for assessment of multibacillary leprosy cases under multidrug therapy. Indian J Dermatol Venereol Leprol 1991;57:22-4

How to cite this URL:
Naik S S, Ganapati R. Use of modified Ridley's bacteriological scale for assessment of multibacillary leprosy cases under multidrug therapy. Indian J Dermatol Venereol Leprol [serial online] 1991 [cited 2020 Jul 14];57:22-4. Available from:

Ridley's Bacteriological index (BI) [1] is used universally to judge bacteriological assessment of multibacillary cases. It is a logarithmic scale and thus a rise in BI from 1 to 2 is not just an addition of one unit but it implies multiplication by a factor of 10. By considering this factor, "scoring point" system, corresponding to Bac­teriological Index, is prepared in order to judge bacteriological quantum in individuals. The effect of multidrug therapy on this quantum over a period of 2 to 5 years is used to asses the overall progress in leprosy control in the given area.

  Material and methods Top

The "scoring points" corresponding to Ridley's Bacteriological index scale are explained in [Table - 1]. An average BI of leprosy patients cannot be more than 6 and hence this grading is not included in table.

To judge the total quantum in human sources in a given community, a modification to Ridley's BI scale is suggested by applying the following formula :

Average BI of patients of each group X No. of patients in the group X "scoring points" of corresponding group = Bacterial Quantum.

By using respective multiplication fac­tor in each BI group, the total bacterial quan­tum in any given community can be gauged in a more striking manner. Even in an individual patient, the bacterial quantum can be worked out and added to the "pool" of number of smear positive cases. For example let us imagine that there are some patients staying in a village, among whom one is having BI 4.2, 2 are having average BI of 3.4 and one has BI 2.6 and 4 others have average BI of 1.2 at any particular period of time. The total bacterial quantum in the village at that point of time will be worked out as follows : given in [Table - 2].

This arithmetic scale to judge bacterial quantum derived from human sources is ap­plied to two situation where multidrug therapy is in progress since 1982 as per the recom­mendation of Indian Association of Leprologists (1982) [3]sub . (i.e.) 600 mg rifampicin + 300 mg clofazimine + 100 mg DDS daily during initial 14 days and (i) monthly supervised "pulse" doses 600 mg rifampicin + 300 mg clofazimine + 100 mg DDS thereafter along with (ii) self administered daily doses of 50 mg clofazimine + 100 mg DDS. One situation is a group of seven leprosy colonies in and around Bombay and the other situation is an urban slum in Bombay. All the patients were screened clini­cally and bacteriological examination was car­ried out every year. The total bacterial quan­tum was estimated by applying the above for­mula.

  Results Top

Due to influx of new multibacillary cases every year the bacterial quantum, though reduced, remained apparently static in this slum even under multidrug therapy for as long as 60 months.

  Comments Top

The application of modified Ridley's Bacteriological scale as suggested by us gives a far better idea about the bacterial quantum in human sources and pooling the results in several individuals in marked area will help to assess the reduction rate of total quantum of bacterial population with the introduction of MDT and thus this indicator will therefore help to assess overall progress of MDT programme in an area where reliable bacteriological exami­nations are available. If proper records of bacteriological examinations are kept, it may also give an idea about the possible epide­miological impact of MDT in long run.

In "super urban" situation like Bombay, the results in leprosy colonies where the entry of new multibacillary cases was restricted the bacterial quantum was reduced remarkably in two years, but in the situations like urban slum where there is no control on influx of new multibacillary cases while the bacterial quan­tum is reduced with MDT as compared to initial state, it remained static even over the period of five years. The results indicate that the leprosy control in such urban slums is not within reach in the near future and this is a grave public health situation.

However, the one factor has to be kept in mind viz. Bacteriological Index is the indi­cator of bacterial load in individual, but it does not give the information regarding the total number of living bacteria. Even accepting the limitation of this fact, using modified Ridley's bacteriological scale and judging the "total bacterial quantum" will still give a proper indi­cation of the progress of MDT program, and the epidemiological situation in any given area.

  References Top

1.Ridley DS : Bacterial Indices. In Leprosy in Theory and Practice Ed. Cochrane R G and Davey T F, Bristol, John Wright and Sons Ltd. 1964, 620-622.  Back to cited text no. 1    
2.Naik SS, Bhanage ND, Sawant KV and Ganapati R : A Bacteriological assessment of multibacillary cases in leprosy colonies after 4 1/2 years of multidrug therapy, Ind J. Leprosy, 1988, 60, 393 399.  Back to cited text no. 2    
3.Indian Association of Leprologists (IAL, 1982) Consensus on treatment regimen in leprosy and problem of drug delivery, Ind J. Leprosy, 1984, 158.  Back to cited text no. 3    


[Table - 1], [Table - 2]


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