Unexpectedly high leprosy seroprevalence detected using a random surveillance strategy in midwestern Brazil: A comparison of ELISA and a rapid diagnostic test

Abstract

Background

Leprosy diagnosis is mainly based on clinical evaluation, although this approach is difficult, especially for untrained physicians. We conducted a temporary campaign to detect previously unknown leprosy cases in midwestern Brazil and to compare the performance of different serological tests.

Methods

A mobile clinic was stationed at the main bus terminal in Brasília, Brazil. Volunteers were quizzed and given a clinical exam to allow categorization as either patients, known contacts of patients or non-contacts, and blood was collected to determine anti-PGL-I and anti-LID-1 antibody titers by ELISA and by the NDO-LID rapid test. New cases of leprosy and the impact of performing this broad random surveillance strategy were evaluated. Accuracy values and concordance between the test results were evaluated among all groups.

Results

Four hundred thirty-four individuals were evaluated, and 44 (10.1%) were diagnosed with leprosy. Borderline forms were the most frequent presentation. Both tests presented higher positivity in those individuals with multibacillary disease. Serological tests demonstrated specificities arround 70% for anti-PGL-1 and anti-LID ELISA; and arround 40% for NDO-LID. Sensitivities ranged from 48 to 62%. A substantial agreement between NDO-LID and ELISA with concomitant positive results was found within leprosy patients (Kappa index = 0.79 CI95% 0.36–1.22).

Conclusions

The unexpectedly high leprosy prevalence in this population indicates ongoing community-based exposure to Mycobacterium leprae antigens and high rates of subclinical infection. All tests showed low specificity and sensitivity values and therefore cannot be considered for use as stand-alone diagnostics. Rather, considering their positivity among MB patients and non-patients, these tests can be considered effective tools for screening and identifying individuals at high risk who might benefit from regular monitoring.

Author summary

Leprosy is a disease that affects the skin and peripheral nervous system, caused by Mycobacterium leprae ( M. leprae), that to survive hides itself within the host cells and grows slowly. Its diagnosis is difficult and requires trained physicians. Laboratorial tests are frequently negative depending on individual response. M. leprae transmission is mainly man to man, because this is very important diagnosis and treatment of patients for breaking the transmission chain. We conducted a temporary campaign to detect previously unknown leprosy cases in midwestern Brazil and to compare the performance of different serological tests (anti-PGL-I and anti-LID-1 antibody titers by ELISA and by the NDO-LID rapid test). Four hundred thirty-four individuals were evaluated, and 44 (10.14%) were diagnosed with leprosy. Each test presented higher positivity in those individuals with multibacillary disease. For leprosy diagnosis, serological tests demonstrated specificities arround 70% for anti-PGL-1 and anti-LID ELISA; and arround 40% for NDO-LID. Sensitivities ranged from 48 to 62%. Anti-PGL-I and anti-LID-1 ELISA sensitivity values were 30.1% and 23.7% respectively, while NDO-LID sensitivity was 51.6% among contacts and non-contacts. The low specificity and sensitivity values of serological tests establish that they cannot be considered stand-alone diagnostics considering the importance of clinical manifestations in leprosy. Rather, we suggest using such tests as a means to triage potential patients for follow-up clinical examinations.