Pertussis: a re-emerging or under diagnosed infectious disease?

very year, mild, self-limited, to severe cases of respiratory nfections are very common, particularly during the winter easons in the South of Brazil. Respiratory viruses are themost ommon causes of these infections. However, bacterial agents ay also be involved. Bordetella pertussis is a well-known cause f respiratory infection,which startswith cold-like symptoms, ut contrary to viral infections, progress to more severe disase that does not resolve even after several weeks. Pertussis is a highly contagious infectious disease, but its pread can be controlled through large-scale vaccination proram. It is noteworthy that vaccination did not eradicate this athogen from the population, although it drastically reduced he number of deaths due to this pathogen. For this reason, . pertussis continues to circulate among our population and s still a cause of whooping cough among infants; especially hose who have not yet received the vaccine or did not comlete the recommended vaccination scheme. Recently, we experienced an increase in the detection of B. ertussis in nasopharyngeal samples of symptomatic patients. rom September to October 2012, 55 nasopharyngeal samples ere submitted to our laboratory for the detection of B. pertusis by real time PCR. The positivity rate was 62%. Patients’ age anged from20days to 8-years-old. Around 30%of the patients ere infants less than one-year-old, while the remaining 70% ere between 4 and 8-years-old. Symptoms were much more evere among infants, often requiring hospitalization. Older hildren tended to have milder symptoms, but still needed edical attention. The main clinical findings were fever and rolonged coughing (>2weeks). Some of the children attended chools were other classmates were also complaining of proonged coughing and cold-like symptoms. In our laboratory, the detection of B. pertussis is done y SYBR-Green-based real time PCR. Primers targeting the S481 repetitive element were designed based on a previous ublication.1 The specificity of the PCR product is checked by elting curve analysis using the LightCycler platform (Roche). o prevent carry-over contamination, all PCR steps were perormed in separated rooms using dedicated materials, and by he use of PCR reagents containing UDG/Glicosylase, which acts to degrade any foreign DNA that may have been accidentally introduced into the reactionmix. Previously, by analyzing 455 nasopharyngeal aspirates from symptomatic children collected between May 2007 and June 2008 as part of project to detect respiratory viruses by real time PCR,2 B. pertussis was found in up 6.4% of those samples (unpublished data), underscoring the importance of this pathogen in our population. Moreover, our data confirm that infants who have not been vaccinated or did not complete the vaccination scheme are at risk for pertussis, and this pathogen should be suspected whenever compatible symptoms are present. The other children that seem to be at risk are those 4–8 years old, whichmay be due to waned immunity towards this pathogen. Although useful for strain characterization, it is well accepted that culture lacks the necessary sensitivity to detect B. pertussis. Molecular methods are replacing culture for the detection of this pathogen, which, besides greater sensitivity, can provide same day results, thus contributing to the correct treatment of the disease and avoiding spread of the bacteria to other persons. Moreover, its exquisite sensitivity can detect the bacteria even after antibiotic treatments or several days after the beginning of the initial symptoms. Whether the increase in the detection rate of B. pertussis represents an increase in the infections associated with this pathogen, as observed in other studies,3 or is simply the result of better detection methods and clinical suspicion remains to be determined. However, it seems clear that the real number of pertussis cases in the South of Brazil may be highly underestimated. Etiology of respiratory diseases is very important for the correct management of the patients. Confirming the presence of a viral agent can prevent the use of unnecessary antibiotics. On the other hand, correctly establishing the presence of bacterial pathogens, such as B. pertussis in a clinical sample from symptomatic patients can substantially reduce the duration of the disease and avoid its spread in the community.