El laboratorio de microbiología ante las enfermedades parasitarias importadas

Time of incubation of agar-plate culture for the diagnosis of Strongyloides stercoralis infection

PURPOSE

Agar-plate culture (APC) remains the most sensitive parasitological technique for S. stercoralis diagnosis. Although it was first described three decades ago, the time of incubation of the plates is neither a commonly described feature nor usually standardized. The aim of the study was to analyze the required time to detect S. stercoralis larvae in APC.

METHODS

A prospective laboratory-based study including all patients with at least one positive APC was performed. The plates were incubated at room temperature for 7 days. Clinical, analytical and parasitological features including results of the direct visualization of the stool (DV) after formalin-ether concentration and time-to-detection (TTD) of the larvae in APC were recorded.

RESULTS

A total of 141 samples from 75 patients had a positive APC. In 49 of them (65.3%) three or more stool samples were processed for direct visualization (DV) and APC. Of these 49 patients, 8 (16.3%) were also diagnosed with DV and 41 (83.7%) were diagnosed only with APC. In 38 samples from 23 (30.7%) patients, the TTD was below 2 days, while in 27 samples from 13 (17.3%) patients, the larvae were detected on the 6th and 7th day.

CONCLUSION

Direct visualization failed to detect S. stercoralis in most of the patients that were diagnosed with APC. Incubation periods below 2 and 5 days would miss an important percentage of infections. At least 7 days of incubation of the APC are required to detect presumably low-burden chronic infections in non-endemic countries.

Paromomycin is superior to metronidazole in Dientamoeba fragilis treatment

Dientamoeba fragilis is a trichomonad parasite of the human intestine that is found worldwide. However, the biological cycle and transmission of this parasite have yet to be elucidated. Although its pathogenic capacity has been questioned, there is increasing evidence that clinical manifestations vary greatly. Different therapeutic options with antiparasitic drugs are currently available; however, very few studies have compared the effectiveness of these drugs. In the present longitudinal study, we evaluate 13,983 copro-parasitological studies using light microscopy of stools, during 2013-2015, in Terrassa, Barcelona (Spain). A total of 1150 (8.2%) presented D. fragilis. Of these, 739 episodes were finally analyzed: those that involved a follow-up parasitology test up to 3 months later, corresponding to 586 patients with gastrointestinal symptoms (53% under 15 years of age). Coinfection by Blastocystis hominis was present in 33.6% of the subjects. Our aim was to compare therapeutic responses to different antiparasitic drugs and the factors associated with the persistence of D. fragilis post-treatment. Gender, age, and other intestinal parasitic coinfections were not associated with parasite persistence following treatment. Metronidazole was the therapeutic option in most cases, followed by paromomycin: 65.4% and 17.5% respectively. Paromomycin was found to be more effective at eradicating parasitic infection than metronidazole (81.8% vs. 65.4%; p = 0.007), except in children under six years of age (p = 0.538). Although Dientamoeba fragilis mainly produces mild clinical manifestations, the high burden of infection means we require better understanding of its epidemiological cycle and pathogenicity, as well as adequate therapeutic guidelines in order to adapt medical care and policies to respond to this health problem.

Rapid diagnosis of gastrointestinal tract infections due to parasites, viruses, and bacteria

Rapid diagnostic techniques are valuable tools in the diagnosis of gastrointestinal infections, especially for the detection of some microorganisms and in certain groups of patients. While antigen detection techniques are widely used in Clinical Microbiology laboratories, for the diagnosis of viruses, some parasites and some bacteria, molecular techniques are routinely used only for some pathogens (such as Clostridium difficile). However, molecular techniques are constantly evolving, and they allow a rapid diagnosis for an increasing number of pathogens, with high sensitivity and specificity. In addition, they are also able to detect virulence factors or resistance mechanisms. Syndromic surveillance systems, which detect different pathogens simultaneously, are very promising because they enable the most frequent pathogens to be diagnosed in a few hours and they can be very useful in certain patients. For the diagnosis of Helicobacter pylori infection, molecular techniques are able to detect bacteria and its resistance to clarithromycin and levofloxacin, allowing the most appropriate treatment to be selected for each patient when bacterial culture is not possible.

Rapid diagnosis of gastrointestinal tract infections due to parasites, viruses, and bacteria

Rapid diagnostic techniques are valuable tools in the diagnosis of gastrointestinal infections, especially for the detection of some microorganisms and in certain groups of patients. While antigen detection techniques are widely used in Clinical Microbiology laboratories, for the diagnosis of viruses, some parasites and some bacteria, molecular techniques are routinely used only for some pathogens (such as Clostridium difficile). However, molecular techniques are constantly evolving, and they allow a rapid diagnosis for an increasing number of pathogens, with high sensitivity and specificity. In addition, they are also able to detect virulence factors or resistance mechanisms. Syndromic surveillance systems, which detect different pathogens simultaneously, are very promising because they enable the most frequent pathogens to be diagnosed in a few hours and they can be very useful in certain patients.

For the diagnosis of Helicobacter pylori infection, molecular techniques are able to detect bacteria and its resistance to clarithromycin and levofloxacin, allowing the most appropriate treatment to be selected for each patient when bacterial culture is not possible.

[Clinical approach to imported eosinophilia]

Eosinophilia is a common finding in international travelers and immigrants, being an helmintic infection its main etiology. The positive predictive value of eosinophilia for an helmintosis is low in travellers. Eosinophilia may be an incidental finding, or symptomatic, and it represents a clinical challenge due to the low sensitivity and specificity of direct and indirect parasitological diagnostic tests, respectively. It requires a structured approach based on geographical areas, environmental exposures and behavioral risks, and associated symptoms. The initial assessment should include a comprehensive and tailored anamnesis and physical examination, basic laboratory tests, a complete parasitological examination of stool samples and a Strongyloides stercoralis serology, supplemented with other explorations guided by epidemiological and clinical suspicion. Empiric treatment with albendazole and/or ivermectin (plus praziquantel if risk of schistosomiasis) is an option for unidentified persistent eosinophilia after study, and in persons in whom a proper assessment or follow-up can not be assured. In patients at risk for estrongiloidosis who are candidates for immunosuppressive therapies, it is indicated a prior screening and treatment to prevent a future hyperinfestation syndrome.

Should we look for Strongyloides stercoralis in foreign-born HIV-infected persons?

The objective was to evaluate the implementation of a systematic Strongyloides stercoralis screening programme in HIV infected immigrants attending an HIV Unit in Spain. An enzyme-linked immunosorbent assay (ELISA) was performed to assess the presence of Strongyloides IgG. Patients with a positive serology were treated with ivermectin; serologic follow-up testing was performed. 237 patients were screened (65.4 % men). Origin: 64.1 % came from Latin America, 16.5 % from Sub-Saharan Africa, 9.7 % from the Caribbean, 9.7 % from other areas. Strongyloides stercolaris IgG was positive in 13 cases (5.5 %). In the multivariate analysis, factors associated with a positive Strongyloides serology were illiteracy (OR: 23.31; p = 0.009) and eosinophilia (OR: 15.44; p < 0.0001). Nine of the 13 patients positive for S. stercoralis IgG and treated with ivermectin had a follow up serologic test: 77.8 % achieved a serologic response (55.5 % seroreversion). Screening of HIV-positive immigrants may be desirable, at least in those with higher risk of hyperinfection syndrome. Serologic testing seems a useful tool in both diagnosis and follow-up of these patients.