Among adults aged 50 years or older, coinfection with respiratory syncytial virus (RSV) and influenza is associated with a 12.1% mortality rate, a new study has found.1 Increasing age, increasing comorbidity burden, and frailty were associated poorer outcomes.1 Henrique Pott, MD, PhD, with Dalhousie University, in Halifax, Canada and Universidade Federal de São Carlos, in São Carlos, Brazil, and colleagues reported their findings in BMC Infectious Diseases.
RSV and influenza virus are important causes of morbidity and mortality whose severity increase with increasing age.2 As with younger patients, the treatment of RSV and influenza in older adults focuses on supportive care.1 However, older adults are more likely to experience severe infections and hospitalizations associated with these infections.1
Although some variability exists in RSV and influenza seasonality based on geographic location, epidemics of these 2 infections often overlap.1 The aim of this study was to examine clinical features and disease presentation, as well as outcomes, for older adults hospitalized with RSV and influenza coinfection.
The surveillance system
The Serious Outcomes Surveillance Network of the Canadian Immunization Research Network (CIRN SOS) is an active surveillance system focusing on influenza infections in Canadian hospitals. This study used data from influenza seasons 2012/2013, 2013/2014, and 2014/2015, during which time respiratory virus testing was performed using a multiplex platform. Active surveillance for influenza infections was conducted in 5 Canadian provinces during the study timeframe.
For this study, data were obtained from CIRN SOS for patients aged 50 years or older who were hospitalized with acute respiratory illness. To be included in the analysis, patient data had to include results from multiplex respiratory virus testing demonstrating coinfection with RSV and influenza, as well as sociodemographic and clinical features and outcomes.
Variables obtained from the database included demographic data, health-related data, and influenza immunization status. The Quan’s Updated Charlson Comorbidity Index score was also calculated, as was a frailty index based on age-dependent disease, disability, and functionality.
Outcomes of interest included overall mortality, 30-day mortality, hospital length of stay, and complications (noninvasive ventilation, mechanical ventilation, and admission to intermediate or intensive care units).
Picture of RSV-influenza coinfection in hospitalized patients
Of 8458 patients with multiplex respiratory virus testing during the study period, 7677 had complete data for study inclusion, and 3644 had positive results on respiratory virus testing. Ninety percent of positive respiratory virus tests were for influenza. Only 33 cases of RSV and influenza coinfection were detected.
Coinfected patients had a median age of 73 years, and most were females. Among patients aged older than 65 years, 66.7% were female, and the median age was 80.5 years. Most patients lived in private community housing and were non-smokers. Only 15.2% of patients had a high mortality risk (based on a comorbidity score of greater than 4). Frailty was present in more than half of patients; this group required regular support for activities of daily living. Most patients reported receiving influenza immunization at some point in the past, and most received antiviral treatment during the hospitalization associated with RSV and influenza coinfection.
Clinical pictures most commonly included cough (81.8%), shortness of breath (66.7%), sputum production (45.5%), weakness (33.3%), fever (27.3%), and nasal congestion (24.2%). Less common signs and symptoms included altered consciousness, chills, headache, nausea, anorexia, malaise, and muscle aches.
With respect to outcomes, the median hospital length of stay was 9 days (range, 2 to 148 days). The mortality rate was 12.1%, and all patients who died did so after at least 20 days of hospitalization. More than one-quarter (27.1%) of patients hospitalized with RSV and influenza coinfection experienced ≥1 complication. Intensive care unit admission was required for 21.2%, whereas mechanical ventilation was needed by 15.2% and noninvasive ventilation by 9.1%.
Among those aged 65 years or older, the mortality rate was 16.7%, and hospital length of stay was 14.5 days. Intensive care unit admission was required for 29.2% of those aged 65 years or older.
An analysis that included demographic and clinical features showed that frailty was associated with 30-day mortality (P=.03).
Limitations
The authors noted that the sample size of patients with co-infection is small, so caution should be taken before generalizing these results. Some sites in the CIRS SOS Network did not use multiplex testing and were therefore not included, leading to potential bias in epidemiological interpretations. Also, nasal swabs were used, which only focus on the upper respiratory tract, so those infected in the lower tract could have shown up negative and been excluded. Finally, end-point, not real-time, RT-PCR testing was used, which is less sensitive and could also have given false negatives. Nevertheless, the study authors noted that the number of patients admitted to the CIRN SOS network was large (>13,000), and more than half (55.4%) received multiplex testing.
In context
The mortality rate found in this study is greater than those previously reported for single respiratory virus infections among older hospitalized adults.1 In addition to overall increased mortality, adults over age 65 with medical comorbidities were more likely to require longer durations of hospitalization and encounter higher complication rates during their hospital course.
The study team emphasized that “coinfection is indistinguishable from isolated infection with other respiratory viruses regarding symptomatology.” Thus, establishing the existence of coinfection with RSV and influenza based on clinical features alone is very difficult. Furthermore, clinicians may miss the existence of coinfection because they stop looking for additional infections following a single positive result, a so-called search-satisfaction bias.
The study team concluded that it is “essential to consider comprehensive testing strategies to detect cases of coinfection,” particularly as virus-specific prevention and treatment approaches become increasingly available.1
Published:
Jennifer Logan is a Preventive Medicine and Public Health-trained physician with 17 years of experience as a medical writer. Her experience as a physician, educator, and researcher helps her write about a wide range of medical subject areas.
