Rapid diagnostic tests for influenza

Rapid and sensitive method using multiplex real-time PCR for diagnosis of infections by influenza a and influenza B viruses, respiratory syncytial virus, and parainfluenza viruses 1, 2, 3, and 4

Laboratory diagnosis of viral respiratory infections is generally performed by virus isolation in cell culture and immunofluorescent assays. Reverse transcriptase PCR is now recognized as a sensitive and specific alternative for detection of respiratory RNA viruses. A rapid real-time multiplex PCR assay was developed for the detection of influenza A and influenza B viruses, human respiratory syncytial virus (RSV), parainfluenza virus 1 (PIV1), PIV2, PIV3, and PIV4 in a two-tube multiplex reaction which used molecular beacons to discriminate the pathogens. A total of 358 respiratory samples taken over a 1-year period were analyzed by the multiplex assay. The incidence of respiratory viruses detected in these samples was 67 of 358 (19%) and 87 of 358 (24%) by culture and real-time PCR, respectively. Culture detected 3 influenza A virus, 2 influenza B virus, 57 RSV, 2 PIV1, and 2 PIV3 infections. All of these culture-positive samples and an additional 5 influenza A virus, 6 RSV, 2 PIV1, 1 PIV2, 1 PIV3, and 3 PIV4 infections were detected by the multiplex real-time PCR. The application of real-time PCR to clinical samples increases the sensitivity for respiratory viral diagnosis. In addition, results can be obtained within 6 h, which increases clinical relevance. Therefore, use of this real-time PCR assay would improve patient management and infection control.

Sensitivity of respiratory virus culture when screening with R-mix fresh cells

Use of R-Mix Fresh Cells has been shown to be a rapid and sensitive method for the detection and identification of respiratory viruses. We prospectively evaluated the impact of incorporation of R-Mix shell vials on the sensitivity and time to detection of seven respiratory viruses recovered in a comprehensive culture during the course of an entire respiratory season in a high-volume clinical laboratory. In this study, R-Mix shell vials were used as part of the culture of 3803 respiratory specimens. A total of 428 respiratory viruses were recovered. Staining of R-Mix vials after overnight incubation allowed initial detection of 274 of 279 influenza viruses, 33 of 38 parainfluenza viruses, 35 of 51 adenoviruses, and 52 of 60 respiratory syncytial viruses (RSVs). The time to reporting of all positive cultures after in-lab specimen receipt was 2.9 days on average and those initially detected in R-Mix cells were reported in 2.3 days on average. A combination of direct fluorescent-antibody (DFA) staining and virus culture was performed on a subset of 711 respiratory specimens. Of 152 viruses identified, 57 were observed only with DFA testing (55 RSV and 2 influenza A viruses) and 31 were recovered only in cell culture. After overnight incubation, R-Mix cells detected 87.1% of respiratory viruses not observed by DFA testing and 96.9% of viruses positive by both methods. The sensitivities of DFA testing and R-Mix cells for identification of influenza viruses were 70.5% and 96.7%, respectively. The R-Mix method detected influenza virus in 18 samples that were negative by DFA testing.

Current challenges in lower respiratory infections in children

PURPOSE OF REVIEW

Lower respiratory infections threaten the health of children worldwide. Streptococcus pneumoniae remains the most common bacterial cause of lower respiratory infection in children, whereas viral pathogens dominate as a more common cause of lower respiratory infection illness in infants and children overall. The diagnosis and clinical management of lower respiratory infections pose challenges to pediatric health providers as new technology is developed and new pathogens emerge in the spectrum of clinical disease.

RECENT FINDINGS

Human metapneumovirus is now recognized as a cause of lower respiratory infection disease in children, and coronavirus has been linked to epidemics of severe acute respiratory syndrome. Respiratory syncytial virus continues to be a major source of viral lower respiratory infection illness in children and can lead to childhood asthma. Treatment for respiratory syncytial virus bronchiolitis depends largely on the severity of disease and the course of clinical symptoms. The diagnosis of bacterial lower respiratory infection disease remains a clinical challenge, but new methods to detect S. pneumoniae, or Chlamydia pneumoniae and Mycoplasma pneumoniae may facilitate the clinical management of these illnesses. As immunization against S. pneumoniae becomes more widely used, the complications of bacterial lower respiratory infections will diminish markedly.

SUMMARY

Future progress in the clinical management of lower respiratory infection diseases will entail improved methods of early diagnosis, broader options for treatment, and better defined clinical parameters for triage and follow-up of children with lower respiratory infections.

Antigenic and molecular analysis of influenza A (H3N2) virus strains isolated from a localised influenza outbreak in South Africa in 2003

A severe acute institutional influenza outbreak occurred in a police residential college in Pretoria amongst new recruits and staff members at the end of May 2003. The outbreak was characterised by marked illness which affected a total of 648 students, 26 of whom were admitted to hospital. Symptoms included pyrexia, severe headache, and myalgia. The attack rate per dormitory building ranged from 20 to 47%, with an overall attack rate of 34%. Throat swabs and bronchoalveolar lavage specimens were sent to the National Institute for Communicable Diseases (NICD) from 20 patients. All were positive for influenza A by multiplex PCR and/or indirect immunofluorescence, and were further identified as subtype H3N2. Additional specimens from sporadic influenza cases in Johannesburg and surrounding areas were collected through the NICD active viral surveillance programme for respiratory viral testing and were also positive for influenza A H3N2 viruses. Viruses isolated from patients from both the institutional outbreak as well as from sporadic cases were analysed both antigenically and at the molecular level to determine the characteristics of the influenza strain responsible for the epidemic. The results showed clearly that the outbreak was caused by the introduction in 2003 into South Africa of the novel A/Fujian/411/02-like H3N2 influenza strain, which is antigenically distinct from the A/Panama/2007/99 vaccine strain. The rapid spread of these variant viruses to the southern hemisphere indicates that the H3N2 component of the influenza vaccine needs to be updated for the 2004 southern hemisphere winter.