Does the length of specimen storage affect influenza testing results by real-time reverse transcription-polymerase chain reaction? an analysis of influenza surveillance specimens, 2008 to 2010.

In some influenza surveillance systems, timely transport to laboratories for reverse transcription-polymerase chain reaction (RT-PCR) testing is challenging.Guidelines suggest that samples can be stored at 4°Cfor up to 96 hours but the effect of longer storage times has not been systematically evaluated. We collected nasopharyngeal and oropharyngeal specimens from patients in Kenya and stored them in viral transport medium at 2 to 8°C before testing for influenza A and B using real-time RT-PCR. From April 2008 to November 2010, we collected 7,833 samples; 940 (12%) were positive for influenza. In multivariable analysis, specimens stored for six days were less likely to be influenza-positive compared to specimens stored between zero and one day (adjusted odds ratio (a OR): 0.49, 95%confidence interval (CI): 0.27­0.93). There was no statistically significant difference in influenza positivity of specimens stored for five days compared to zero to one day. There was no statistically significant relationship between days in refrigeration and cycle threshold(Ct) values for positive samples (p=0.31). We found that samples could remain in storage for at least five days without affecting the proportion-positive of samples,potentially increasing the feasibility of including influenza surveillance sites in remote areas.

What are the most sensitive and specific sign and symptom combinations for influenza in patients hospitalized with acute respiratory illness? Results from western Kenya, January 2007-July 2010.

Influenza causes severe illness and deaths, and global surveillance systems use different clinical case definitions to identify patients for diagnostic testing. We used data collected during January 2007-July 2010 at hospital-based influenza surveillance sites in western Kenya to calculate sensitivity, specificity, positive predictive value, and negative predictive value for eight clinical sign/symptom combinations in hospitalized patients with acute respiratory illnesses, including severe acute respiratory illness (SARI) (persons aged 2-59 months: cough or difficulty breathing with an elevated respiratory rate or a danger sign; persons aged ≥5 years: temperature ≥38 °C, difficulty breathing, and cough or sore throat) and influenza-like illness (ILI) (all ages: temperature ≥38 °C and cough or sore throat). Overall, 4800 persons aged ≥2 months were tested for influenza; 416 (9%) had laboratory-confirmed influenza infections. The symptom combination of cough with fever (subjective or measured ≥38 °C) had high sensitivity [87·0%, 95% confidence interval (CI) 83·3-88·9], and ILI had high specificity (70·0%, 95% CI 68·6-71·3). The case definition combining cough and any fever is a simple, sensitive case definition for influenza in hospitalized persons of all age groups, whereas the ILI case definition is the most specific. The SARI case definition did not maximize sensitivity or specificity.

The natural history of respiratory syncytial virus in a birth cohort: the influence of age and previous infection on reinfection and disease.

This study aimed to quantify the effect of age, time since last infection, and infection history on the rate of respiratory syncytial virus infection and the effect of age and infection history on the risk of respiratory syncytial virus disease. A birth cohort of 635 children in Kilifi, Kenya, was monitored for respiratory syncytial virus infections from January 31, 2002, to April 22, 2005. Predictors of infection were examined by Cox regression and disease risk by binomial regression. A total of 598 respiratory syncytial virus infections were identified (411 primary, 187 repeat), with 409 determined by antigen assay and 189 by antibody alone (using a "most pragmatic" serologic definition). The incidence decreased by 70% following a primary infection (adjusted hazard ratio = 0.30, 95% confidence interval: 0.21, 0.42; P < 0.001) and by 59% following a secondary infection (hazard ratio = 0.41, 95% confidence interval: 0.22, 0.73; P = 0.003), for a period lasting 6 months. Relative to the age group <6 months, all ages exhibited a higher incidence of infection. A lower risk of severe disease following infection was independently associated with increasing age (P < 0.001) but not reinfection. In conclusion, observed respiratory syncytial virus incidence was lowest in the first 6 months of life, immunity to reinfection was partial and short lived, and disease risk was age related.