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Please cite this paper as: Goka et al. (2013) Influenza A viruses dual and multiple infections with other respiratory viruses and risk of hospitalisation and mortality. Influenza and Other Respiratory Viruses 7(6), 1079–1087. Introduction Recent literature suggests that dual or multiple virus infections may affect disease severity. However, few studies have investigated the effect of co‐infection with influenza A viruses. Objectives To identify the association between influenza A and respiratory viruses co‐infections with disease outcome. Methodology Data for samples from North West England tested between January 2007 and June 2011 was analysed for patterns of co‐infection between influenza A viruses and eight respiratory viruses. Risk of hospitalisation to ICU or general ward in single versus co‐infections was assessed using logistic regression. Results Of the 25 596 samples analysed for respiratory viruses 40·7% (10 501) were positive for any virus. Co‐infections were detected in 4·7% (137/2879) of all patients with influenza A(H1N1)pdm09, and 7·3% (57/779) of those with other influenza A virus infections. Co‐infection between seasonal influenza A viruses and influenza B virus was associated with a significant increase in the risk of admission to ICU/death (OR: 22·0, 95% CI: 2·21–219·8, P = 0·008). Respiratory syncytial virus/influenza A (RSV/Flu A) co‐infection also increased this risk but was not statistically significant. For influenza A(H1N1)pdm09, RSV and AdV co‐infection increased risk of hospitalisation to general ward whereas Flu B increased risk of admission to ICU, but none of these were statistically significant. Conclusion Co‐infection is a significant predictor of disease outcome; combined treatment, introduction of an integrated vaccine for all respiratory viruses and development of multi‐target rapid diagnostic tests is recommended. Integration of respiratory viruses’ co‐infections into public health reports could also contribute to the accumulation of evidence.

Respiratory virus infections cause a significant number of hospitalization and deaths globally. This study investigated the association between single and multiple respiratory virus infections and risk of admission to a general ward, intensive care unit or death in patients aged 0-105 years (mean ± s.d. = 24·4 ± 24·1 years), from North West England, that were tested for respiratory virus infections between January 2007 and June 2012. The majority of infections were in children aged ⩽5 years. Dual or multiple infections occurred in 10·4% (1214/11 715) of patients, whereas single infection occurred in 89·6% (10 501/11 715). Rhinovirus was the most common co-infecting virus (occurring in 69·5%; 844/1214 of co-infections). In a multivariate logistic regression model, multiple infections were associated with an increased risk of admission to a general ward [odds ratio (OR) 1·43, 95% confidence interval (CI) 1·2-1·7, P < 0·0001]. On the other hand, patients with respiratory syncytial virus (RSV) and human parainfluenza virus types 1-3 (hPIV1-3), as a single infection, had a higher risk of being admitted to a general ward (OR 1·49, 95% CI 1·28-1·73, P < 0·0001 and OR 1·34, 95% CI 1·003-1·8, P = 0·05, respectively); admitted to an intensive-care unit or dying (OR 1·5, 95% CI 1·20-2·0, P = 0·001 and OR 1·60, 95% CI 1·02-2·40, P = 0·04, respectively). This result emphasizes the importance of RSV, hPIV and mixed infections and calls for research on vaccines, drugs and diagnostic tests targeting these respiratory viruses.

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