Endemic to Latin America, paracoccidioidomycosis (PCM) is a human disease with high incidence in Brazil, Venezuela, Colombia and Argentina (Blotta

Endemic to Latin America, paracoccidioidomycosis (PCM) is a human disease with high incidence in Brazil, Venezuela, Colombia and Argentina (Blotta et al. 1999). PCM is caused by the thermo-regulated dimorphic fungus Paracoccidioides brasiliensis (Manns et al. 1996). The definitive diagnosis of PCM is made by identifying budding yeast in biopsies or other pathological material. However, the fungus is difficult to observe in many cases; diagnosis is often performed through serological assays (Mendes-Gianinni et al. 1994). Several serological assays have been used for the early diagnosis of PCM. However, a standard diagnostic method has been difficult to establish because of variation in assay sensitivity, specificity and reproducibility (Camargo 2008). Double immunodiffusion (ID) is the most frequently used test for the immunodiagnosis of PCM and the use of Ag7 as an antigenic preparation standard is believed to be necessary for a successful diagnosis with this methodology (Camargo et al. 2003). Despite its low complexity, few laboratories can use ID for routine diagnosis. Nevertheless, countries and endemic areas with poor infrastructure require more executable methods at the clinical level. The latex agglutination test (LAT), a slide agglutination test for the serodiagnosis of PCM, was described primarily in the 1970s, but the results obtained with this assay were inconclusive (Restrepo & Moncada 1978). Recently, our laboratory evaluated LAT to detect antibodies against P. brasiliensis in the sera of patients with both clinical forms of PCM (Silveira-Gomes et al. 2011) and the sensitivity and specificity rates obtained were 84% and 81%, respectively. Cross-reactivity was observed with pulmonary fungal [aspergillosis (ASP) and histoplasmosis (HP)] and bacterial infections. The serodiagnosis of cryptococcosis led to the use of LAT in the immunological diagnosis of fungal infections (Bloomfield et al. 1963). However, this accomplishment was only possible because interfering factors could be detected and then corrected for, which allowed for high performance of the assay. Several studies use different methods to minimize the effect of interfering factors while performing these tests. The mostly widely used technique is the prior inactivation of serum to avoid the interference of complement and other serum proteins in the assay (Stockman & Roberts 1983). The inactivation of samples prior to testing is critical for complement fixation (Almeida & Cunha 1981), but it is still unclear how inactivation influences the efficacy of LAT to detect antibodies against P. brasiliensis. In our previous study, all serum samples were tested in their fresh forms, which is the same procedure used in the gold standard test (ID test). The aim of the current study was to describe the influence of prior the inactivation of serum samples on the performance of LAT for detecting antibodies against PCM. A total of 30 PCM patients with diagnoses established by either direct examination (n = 4) or positive serological ID tests (n = 26) were included in this study. This population was composed of 26 males and four females aged 22-75 years. Approximately 10% of the patients presented with the acute form of the disease, while 90% had the chronic form. Heterologous serum samples of patients with HP (n = 6), ASP (n = 5) and non-fungal disease (NFD) (patients presenting bacterial infections; n = 49) were used. Eleven serum samples from healthy individuals with no history of pulmonary disease were also studied as negative controls and were termed normal human sera (NHS). All serum specimens were divided into aliquots and were stored at -20oC. Serum samples were inactivated by incubation at 56oC for 30 min prior to testing. Financial support: CNPq (471106/2007-0) + Corresponding author: marquespb339@gmail.com Received 6 July 2011 Accepted 8 November 2011 Effect of serum sample inactivation on the performance of latex agglutination test for paracoccidioidomycosis serodiagnosis