Abstract
BackgroundLeprosy transmission is ongoing; globally and within Bangladesh. Household contacts of leprosy cases are at increased risk of leprosy development. Identification of household contacts at highest risk would optimize this process.MethodsThe temporal pattern of new case presentation amongst household contacts was documented in the COCOA (Contact Cohort Analysis) study. The COCOA study actively examined household contacts of confirmed leprosy index cases identified in 1995, and 2000–2014, to provide evidence for timings of contact examination policies. Data was available on 9527 index cases and 38303 household contacts. 666 household contacts were diagnosed with leprosy throughout the follow-up (maximum follow-up of 21 years). Risk factors for leprosy development within the data analysed, were identified using Cox proportional hazard regression.FindingsThe dominant risk factor for household contacts developing leprosy was having a highly skin smear positive index case in the household. As the grading of initial slit skin smear of the index case increased from negative to high positive (4–6), the hazard of their associated household contacts developing leprosy increases by 3.14 times (p<0.001). Being a blood relative was not a risk factor, no gender differences in susceptibility were found.InterpretationWe found a dominance of a single variable predicting risk for leprosy transmission–skin smear positive index cases. A small number of cases are maintaining transmission in the household setting. Focus should be performing contact examinations on these households and detecting new skin smear positive index cases. Conducting slit-skin smears on new cases is needed for predicting risk; such services need supporting. If skin smear positive cases are sustaining leprosy infection within the household setting, the administration of single-dose rifampicin (SDR) to household contacts as the sole intervention in Bangladesh will not be effective.
Highlights
Household contacts of leprosy cases are at increased risk of leprosy development
Targeted household examinations could increase early case detection: this is important because untreated leprosy cases are sustaining transmission
We found a single dominant risk factor for the development of leprosy in the household setting, namely slit skin smear positivity in the index case
Summary
Granulomatous disease caused by the intracellular bacterium Mycobacterium leprae (M. leprae).[1, 2] An infection of the skin and peripheral nerves, [3, 4] the incubation period is variable—from months up to 30 years. [2] The main route of infection is via the airways/ oronasal mucous membranes. [2] Leprosy is microbiologically curable; early case detection and treatment with multi-drug therapy (MDT) reduces risk of risk of onward transmission and development of disability. [5] Cure rates with modern MDT are very high and relapse rates are low. [2, 6] Leprosy has significant social and psychological implications. [7] Stigma is an important cause of delayed diagnosis. [8, 9] Leprosy exhibits a clustered distribution at the household (HH)/ social interaction level. [10]Around 210,000 new cases are detected annually globally, with little change over the last ten years. [11] Currently 80% of newly detected cases occur within five countries. [1, 3] Bangladesh ranks fifth globally amongst newly detected cases. [12, 13]The epidemiology of leprosy and mode of transmission of infection remains poorly understood. [20] Early case detection and treatment reduces further transmission of infection and helps prevent development of Grade-2 disabilities. The Leprosy Field Research in Bangladesh (LFRB) project is a leprosy control programme covering four districts in NW-Bangladesh with a total population of approximately 7.5 million; the project works as part of the non-governmental organisation The Leprosy Mission International, Bangladesh (TLMIB) Data from this routine surveillance period was used with further data from a cross sectional survey completed in 2015/16. Compared to the rest of the country, NW-Bangladesh has a high PB rate, and has similar climate, environment and geography This high PB rate is probably due to the intervention effect; the area has a well-established leprosy control unit engaged with leprosy research for over 20 years. Identification of household contacts at highest risk would optimize this process
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