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Deciphering Microscopic Agglutination Test (MAT) Serogroup Cross-Reactivity in Leptospirosis: The Influence of Age
Eric J Nilles1,2,3, Cecilia Then Paulino4, William Duke5
1Brigham and Women's Hospital, Boston, MA 02115, USA.
Abstract:
Leptospirosis is a zoonotic disease caused by Leptospira spp., with over 250 serovars classified into 24 serogroups. Control measures depend on understanding serovar-specific epidemiology, yet the microscopic agglutination test (MAT) is only serogroup specific, and classification is complicated by cross-reactivity. While MAT is the reference standard for leptospirosis serodiagnosis and seroepidemiological studies, factors influencing serogroup cross-reactivity remain poorly characterized. We investigated the relationship between age, antibody titer, and serogroup diversity among seropositive individuals in a population-based serosurvey in the Dominican Republic. Between June and October 2021, we conducted a multistage national serosurvey, enrolling 6683 participants across 134 clusters. MAT was performed on sera from 2091 participants in two provinces using a 20-serovar panel. MAT positivity was defined as titers ≥ 1:100. Generalized Additive Models were used to assess associations between age, maximum titer, and serogroup diversity. Of 2091 tested samples, 237 (11.3%) were seropositive. Older individuals and those with higher titers reacted to a greater number of serogroups (p = 0.005 and p < 0.0001, respectively). However, mean maximum titer decreased with age, suggesting that broader serogroup reactivity in older individuals reflects cumulative exposure rather than higher titers. Maximum titer was the strongest predictor of serogroup breadth, while gender, study region, and urban/rural setting were not significant. Overall, our findings demonstrate that serogroup cross-reactivity in MAT was significantly influenced by antibody titer and prior exposure, with older individuals displaying broader serogroup reactivity despite lower titers. These findings highlight key considerations for interpreting MAT results in seroepidemiological studies and underscore the limitations of MAT in serogroup-level classification.
Insights
Leptospirosis serogroup cross-reactivity in the microscopic agglutination test (MAT) is influenced by antibody titer and cumulative exposure. Older individuals show broader reactivity, highlighting MAT limitations for serogroup classification.
Area of Science:
- Infectious Diseases
- Epidemiology
- Immunology
Background:
- Leptospirosis, a zoonotic disease caused by *Leptospira* spp., presents diagnostic challenges due to over 250 serovars and serogroup cross-reactivity in serological tests.
- The microscopic agglutination test (MAT) is the gold standard for leptospirosis diagnosis but its serogroup specificity is limited by cross-reactivity, complicating epidemiological studies.
Purpose of the Study:
- To investigate the impact of age and antibody titer on serogroup diversity and cross-reactivity in leptospirosis serological testing.
- To understand factors influencing serogroup breadth in seropositive individuals within a population-based survey.
Main Methods:
- A population-based serosurvey was conducted in the Dominican Republic with 6683 participants.
- Microscopic agglutination test (MAT) was performed on 2091 sera using a 20-serovar panel, defining positivity at titers ≥ 1:100.
- Generalized Additive Models assessed associations between age, maximum titer, and serogroup diversity.
Main Results:
- 11.3% (237/2091) of participants tested were seropositive for leptospirosis.
- Older individuals and those with higher antibody titers reacted to a greater number of serogroups (p=0.005 and p<0.0001, respectively).
- Maximum titer strongly predicted serogroup breadth, while age was associated with broader reactivity despite lower mean titers, suggesting cumulative exposure.
Conclusions:
- Serogroup cross-reactivity in MAT for leptospirosis is significantly influenced by antibody titer and cumulative exposure history.
- Older individuals exhibit broader serogroup reactivity, indicating past exposure rather than current high-titer infection.
- Findings emphasize the need for careful interpretation of MAT results in seroepidemiological studies and highlight limitations in serogroup-level classification.
