PracticeUpdate Cardiology June 2019

EDITOR’S PICKS 10

Association of Influenza-Like Illness Activity With Hospitalizations for Heart Failure JAMA Cardiology

Take-home message • The authors evaluated the association between influenza activity and hospitaliza- tions for heart failure (HF) or myocardial infarction (MI) between 2010 and 2014. A 5% increase in influenza activity was associated with a 24% increase in the rate of HF hospitalizations. The same association was not seen for MI hospitalizations. • Influenza activity may contribute to the risk of HF hospitalization among community- dwelling adults. COMMENT By Jonathan Temte MD, PhD Congestive Heart Failure Hospitalization and Influenza-Like Illnesses S o far this year, 1 of every 600, or nearly 80,000, individuals aged 65 years or older has been hospitalized due for heart failure (HF). Influenza infection may increase metabolic demands, acti- vate the sympathetic nervous system, trigger proinflammatory cytokines, or cause volume overload – all factors that could contribute to exacerbations of HF. A recent study links ILI prevalence in pri- mary care to HF hospitalizations.

Abstract IMPORTANCE Influenza is associated with an increased risk of cardiovascular events, but to our knowledge, few studies have explored the temporal association between influenza activity and hospitalizations, especially those caused by heart failure (HF). OBJECTIVE To explore the temporal association between influenza activity and hospitalizations due to HF and myocardial infarction (MI). We

HF and myocardial infarction (MI) in four communities with the monthly ILI across four influenza seasons (2010–2014). Analyses were adjusted for outside tem- perature, sex of patient, race, age, and region. A very large and significant 24% increase in HF was associated with a 5% absolute rise in ILI (eg, from 1% to 6%). Overall, the adjusted incidence rate ratio was 1.24 (95% CI, 1.11–1.38) for the pooled anal- ysis. On the other hand, no increased risk for MI was noted (aIRR, 1.02; 95% CI, 0.90–1.17). In this study, the authors were not able to assess any association with vaccination status. Moreover, there was no direct assessment of influenza in the patients, leaving the possibility that other infections, such as respiratory syncytial virus or human metapneumovirus, could also contribute to this effect. This study adds to existing evidence by showing that increases in prevalence of influenza, as indicated by increases in ILI, are associated with increases in cardio- vascular hospitalization. Moreover, efforts to reduce the spread of influenza may result in reduced morbidity, hospitaliza- tion, and mortality. Reference 1. FluView. 2018-2019 Influenza Season Week 12 ending March 23, 2019. Available at: www.cdc. gov/flu/weekly. Accessed April 3, 2019.

to influenza. We are in the midst of our seasonal influenza outbreak, but the nation- wide prevalence of influenza-like illness (ILI) is declining. 1 ILI – defined as a fever of 100°F (37.8°C) or higher, along with cough and/or sore throat – is a useful construct in primary care-based influenza surveillance. In gen- eral, the prevalence of ILI correlates well with the prevalence of influenza. Although there is much known about the association between cardiovascular mortality and influenza, far less is known about the extent to which influenza contributes to cardiovascular hospitali- zation, and, in particular, hospitalization

The US Outpatient Influenza-like Illness Surveillance Network (ILINet) is run by the CDC, with ample assistance from state and local public health departments. 1 Each week, primary care clinicians report the total number of patients seen and the number of patients with ILI (Figure). Researchers from the Atherosclerosis Risk in Communities study compared the monthly frequency of hospitalization for

Percentage of visits for influenza-like-illness (ILI) reported by the US Outpatient Influenza-like-Illness Surveillance Network (ILINet), Weekly National Summary, 2018–2019 and selected previous seasons.

Dr. Temte is Professor at the University of Wisconsin School of Medicine and Public Health, Department of Family Medicine and

Community Health in Madison, Wisconsin.

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