Sensitivity of diagnostic methods for Mansonella ozzardi microfilariae detection in the Brazilian Amazon Region

<div><p> BACKGROUND The human filarial worm Mansonella ozzardi is highly endemic in the large tributaries of the Amazon River. This infection is still highly neglected and can be falsely negative when microfilariae levels are low. OBJECTIVES This study investigated the frequency of individuals with M. ozzardi in riverine communities in Coari municipality, Brazilian Amazon. METHODS Different diagnostic methods including polymerase chain reaction (PCR), blood polycarbonate membrane filtration (PCMF), Knott's method (Knott), digital thick blood smears (DTBS) and venous thick blood smears (VTBS) were used to compare sensitivity and specificity among the methods. Data were analysed using PCMF and Bayesian latent class models (BLCM) as the gold standard. We used BLCM to calculate the prevalence of mansonelliasis based on the results of five diagnostic methods. FINDINGS The prevalence of mansonelliasis was 35.4% by PCMF and 30.1% by BLCM. PCR and Knott methods both possessed high sensitivity. Sensitivity relative to PCMF was 98.5% [95% confidence interval (CI): 92.0 - 99.7] for PCR and 83.5% (95% CI: 72.9 - 90.5) for Knott. Sensitivity derived by BLCM was 100% (95% CI 93.7 - 100) for PCMF, 100% (95% CI: 93.7 - 100) for PCR and 98.3% (95% CI: 90.6 - 99.9) for Knott. The odds ratio of being diagnosed as microfilaremic increased with age but did not differ between genders. Microfilariae loads were higher in subjects aged 30 - 45 and 45 - 60 years. MAIN CONCLUSIONS PCMF and PCR were the best methods to assess the prevalence of mansonelliasis in our samples. As such, using these methods could lead to higher prevalence of mansonelliasis in this region than the most commonly used method (i.e., thick blood smears).</p></div

Algorithm of the study, describing the details of eligible, enrolled and analyzed children.

<p>Algorithm of the study, describing the details of eligible, enrolled and analyzed children.</p

Baseline characteristics of 54 schoolchildren followed from April to November 2008, in an endemic area for malaria (municipality of Careiro, Amazonas, Brazil), according to the helminth detected at stool examination during <i>P. vivax</i>.

<p>Baseline characteristics of 54 schoolchildren followed from April to November 2008, in an endemic area for malaria (municipality of Careiro, Amazonas, Brazil), according to the helminth detected at stool examination during <i>P. vivax</i>.</p

Correlation between parasitemia and hemoglobin.

<p>Correlation between parasitemia and hemoglobin during the first malarial attack in children without helminthes (A) and with helminthes (B).</p

Mean (± standard error of the mean) hemoglobin concentration before (baseline Hb) and during (malarial Hb) the first <i>P. vivax</i> acute attack in 54 schoolchildren followed from April to November 2008, in an endemic area for malaria (Municipality of Careiro, Amazonas, Brazil), according to the helminth detected at stool examination.

<p>Mean (± standard error of the mean) hemoglobin concentration before (baseline Hb) and during (malarial Hb) the first <i>P. vivax</i> acute attack in 54 schoolchildren followed from April to November 2008, in an endemic area for malaria (Municipality of Careiro, Amazonas, Brazil), according to the helminth detected at stool examination.</p

Survival analysis of the time for the first malarial episode.

<p>Kaplan-Meier survival analysis showing the time elapsed from the baseline cross-sectional to the first malarial infection (in days) in 54 schoolchildren followed from April to November 2008, with and without <i>Ascaris lumbricoides</i> (A), hookworm (B) and <i>Trichuris trichiura</i> (C).</p

Baseline demographic and clinical data of the study participants.

<p>TST: Tuberculin Skin Test, QFT: QuantiFERON-TB Gold In-Tube, MTC-score: <i>Mycobacterium tuberculosis</i> contact score, BCG: Bacillus Calmette-Guérin.</p>#<p>Categorical variables expressed as number of subjects (n) and percentage (%) compared to those evaluated with the characteristic studied. Quantitative variables expressed as mean and interquartile range (IQR).</p>a<p>In the 12 weeks prior to the study.</p>b<p>Risk of malnutrition was defined as a Z score for weight less than −1 SDs for age and gender; malnutrition was defined −2 SDs for age and gender.</p

Multivariate logistic regression according to factors for positive QFT results stratified by TST results.

<p>TST: Tuberculin Skin Test, QFT: QuantiFERON-TB Gold In-Tube, MTC-score: <i>Mycobacterium tuberculosis</i> contact score, BCG: Bacillus Calmette-Guérin.</p>a<p>logistic regression coefficient related to quantitative variable.</p>b<p>Linear odds ratio; exponential to the regression coefficient.</p

Odds ratio and confidence interal of 95% for the Tuberculosis Skin Test positive results according to time of exposure (months) to index case.

<p>Odds ratio and confidence interal of 95% for the Tuberculosis Skin Test positive results according to time of exposure (months) to index case.</p

Bivariate analysis and Multivariate logistic regression for TST results and QFT results.

<p>TST: Tuberculin Skin Test, QFT: QuantiFERON-TB Gold In-Tube, MTC-score: <i>Mycobacterium tuberculosis</i> contact score, BCG: Bacillus Calmette-Guérin.</p>#<p>Categorical variables expressed as percentage (%) and quantitative variables expressed as mean and interquartile range (IQR).</p>a<p>In the 12 weeks prior to the study.</p>b<p>Linear odds ratio.</p