Detection of Helicobacter pylori by Real-Time PCR for 16s rRNA in Stools of NonInfected Healthy Children
Detection of Helicobacter pylori by Real-Time PCR for 16s rRNA in Stools of NonInfected Healthy Children, Using ELISA Antigen Stool Test as the Gold Standard
SUMMARYThe importance of Helicobacter pylori (H. pylori) infection in gastroduodenal disease is well established. However, most infected individuals never experience clinically relevant signs and/or symptoms. Reliable noninvasive diagnostic methods have been developed for H. pylori detection. Antibody-based enzyme-linked immunosorbent assay (ELISA) for H. pylori detection in stools has shown high sensitivity and specificity. Real-time PCR (rt-PCR), meanwhile, is not widely used for stool detection of H. pylori, and results have been variable. Infection status in asymptomatic children is currently categorized into two groups: transient infections or persistent infections.Data of a previous study showed that 33% of ELISA-negative samples were rtPCR positive. So, the authors aimed to determine whether persistent infections could be accurately detected by rtPCR, despite the possibility of false ELISA negative results. For the purpose, ELISA antigen stool tests were used as “gold standard”, and rtPCR for 16s rRNA as the test method. The study was based on two previous prospective cohort studies of Chilean children: the authors selected 36 subjects with an ELISA-negative/rtPCR-positive stool sample. 25 of these children had never been infected with H. pylori and 11 had a transient infection.To determine the proportion of these children with a possible persistent infection detectable only by rtPCR, two to three ELISA-negative stool samples from each child were tested by rtPCR for 16s rRNA. A total of 78 samples were analyzed. To confirm the reproducibility of the rtPCR protocol, five samples from infected children were reanalyzed by rtPCR: as expected, rtPCR for 16s rRNA was consistently positive. The authors performed 156 rtPCR on ELISA-negative stool samples, of which 14 (18%) were rtPCR positive, but only 4 of 78 (5.1%) samples were consistently positive by rtPCR for 16S rRNA, from a total of 3/36 (8.3%) children who had an initial rtPCR-positive/ELISA-negative sample. Only 4% of noninfected children had one positive sample, in both duplicates, by rtPCR. Two of the eleven children with a transient infection by ELISA (18.1%) had one or two additional rtPCR-positive samples in both duplicates. Overall, rtPCR testing for 16s rRNA was able to detect a possible persistent infection not detected by ELISA in one of 36 (2.7%) children.The authors highlighted that both noninvasive tests, ELISA and rtPCR run in duplicate, are highly concordant when defining the infection status of children, not only for persistently infected children, but also for transient or noninfected children. Although scarce, ELISA-negative/rtPCR-positive samples did occur and their significance remains to be elucidated. Importantly, the majority of positive results occurred in only one of the two duplicates, strongly suggesting that these were false positives. The relatively higher 16S rRNA detection rate in stools from children with a transient infection compared to those who never had an ELISA-positive sample, suggests that the intermittency of bacterial/antigen load in the stools of these children may be playing a role in determining ELISA versus rtPCR positivity. The authors concluded that, despite the need of further research, stool ELISA is a reliable method in characterizing H. pylori dynamics in apparently healthy children.
AUTHORS: George S, Mamani N, Lucero Y, Torres JP, Farfán M, Lagomarcino AJ, Orellana A, O'Ryan M.
Go to the article
Meningococcal disease in Latin America
WAidid suggests this week "The current situation of meningococcal disease in Latin America and updated Global Meningococcal Initiative (GMI) recommendations", the article published on Vaccine at the end of 2015
SUMMARY:Neisseria meningitidis (N. meningitidis) remains a major cause of invasive bacterial disease worldwide and is associated with substantial morbidity and overall case fatality rates of around 10%. In Latin America, incidence rates and serogroup distribution of meningococcal disease (MD) are highly variable and very limited data are available from different countries. The Global Meningococcal Initiative (GMI) is a multidisciplinary group, which aims to help to prevent MD worldwide through education, research, international cooperation, and to develop recommendations.The reporting of MD is mandatory in Latin America, but surveillance systems and reporting systems are not standardized across countries. In addition, there is limited access to hospital care in some countries, as well as differences in the diagnostic methods and MD case definitions.In order to help improve and standardize reporting of MD in Latin America, the GMI has proposed a number of recommendation, including a clear definition of a suspected case, the use of molecular diagnostic techniques in routine surveillance, an expanding use of culture methods, to establish well-equipped sentinel and reference laboratories with highly trained staff, and the adoption of a single case definition in all Latin American countries. Nevertheless, the GMI recognizes that some countries have resource and financial constraints, which prevent them from taking up all recommendations, and it therefore encourages alliances to be formed with other supportive organizations.Monitoring phenotypic and genotypic characteristics of circulating N. meningitidis strains is of fundamental importance in understanding MD in each country. Six serogroups (A, B, C, W, X, and Y) cause nearly all cases of MD globally. Most cases of MD in Latin America are sporadic and caused by serogroups B and C, with emergence of serogroup W in Southern Cone countries. In contrast, serogroup A has virtually disappeared from Latin America.Information about the carriage of N. meningitidis is essential in understanding the transmission dynamics of meningococcal infection, and for assessing the extent and potential that exists for vaccination strategies to induce herd protection.The Chilean experience provides a unique opportunity to learn more about serogroup W disease and about the importance of an integrated surveillance system, a rapid response, and transparent dissemination of data to the public.In late 2010, Brazil became the first Latin American country to introduce Meningococcal C conjugate (MCC), providing an immediate reduction in incidence rates of MD in children aged <2 years, but no early impact was observed in unvaccinated age groups.The authors highlighted that, although notification of MD is compulsory in Latin America, surveillance is inconsistent and that the only countries where there is evidence of routine use of the molecular diagnostic test are Brazil and Chile. The authors concluded that the introduction of meningococcal vaccines across Latin America represents an important achievement in the control of MD, however there remain significant challenges in ensuring that the best strategies, both in terms of public health impact and cost-effectiveness, are being implemented. Finally, they highlighted the importance of vaccine affordability, and consequently, access, and they stressed the marked imbalance existing in the infrastructures and available resources, among the different States.
AUTHORS: Sáfadi M. A., O'Ryan M., Valenzuela Bravo M. T., Brandileone M. C., Gorla M. C., de Lemos A. P., Moreno G., Vazquez J. A., López E. L., Taha M. K., Borrow R.; Global Meningococcal Initiative.