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Atrial fibrillation is a well recognized risk factor for developing complications from influenza, and becoming sick with the flu just may be associated with an increased risk for developing Afib.

In a newly reported nationwide, case-control study from Taiwan, influenza infection was significantly associated with new onset atrial fibrillation (Afib), with study participants who had the flu during the previous year having an 18% increased risk for an Afib diagnosis.

Influenza vaccination was consistently associated with a lower risk for Afib, suggesting that getting a flu shot may reduce at-risk patients' risk for developing the arrhythmia, researcher , of Taipei Veterans General Hospital in Taiwan, and colleagues wrote in the journal , published online.

"The present study represents the first population-based study investigating the association between influenza infection, vaccination, and occurrence of AF," the researchers wrote. "Influenza vaccination may be a useful way to reduce the AF burden associated with influenza infection and high-risk patients should be encouraged to receive influenza vaccination annually."

The study included 11,374 patients with newly diagnosed Afib between 2000 and 2010, identified through a nationwide health insurance database in Taiwan. The National Health Insurance Research Database (NHIRD) contained all medical claims data for a random sample of 1,000,000 beneficiaries of a mandatory health insurance program that provides comprehensive medical coverage to all residents of Taiwan.

Four control patients without Afib, matched for age and sex, were selected for each Afib patient from the NHIRD.

"The database with a large sample size provided an excellent opportunity to study the association between influenza infection, vaccination and the risk of AF," the researchers wrote.

The mean age of the study population was 70 ± 13.4 years, and 55.7% of the patients were male. Compared to controls, Afib patients had more comorbidities, received more medical imaging, and had more outpatient physician visits for upper respiratory tract and influenza infections.

The study revealed a modest but statistically significant association between influenza infection in the prior year and influenza vaccination and Afib.

Specifically:

• Compared to patients without influenza infection who were not vaccinated against the flu (reference group, n=38,353), having influenza infection without vaccination (n=1,369) was associated with a significantly higher risk of Afib with an odds ratio of 1.182 (P=0.032) after the adjustment for baseline differences.

• Atrial fibrillation risk was lower among patients receiving influenza vaccination without influenza infection (n=16,452), with an odds ratio of 0.881 (P<0.001).

• Among patients who received influenza vaccination and experienced influenza infection (n=696), Afib risk was similar to that of the reference group (OR 1.136, P=0.214), and vaccination was consistently associated with lower risk in a subgroup analysis.

In addition to the observational design of the trial, which precluded showing a causal association between influenza infection and higher Afib risk, study limitations cited by the researchers included the lack of information on potentially relevant participant characteristics, including smoking status, physical activity, and BMI.

Neither electrocardiographic validation of Afib diagnosis nor biochemical validation of the influenza diagnosis were available, meaning the researchers had to rely on diagnostic coding for case identification.

"We were not able to conclude whether influenza infection was the direct cause of the increased risk of AF, and only a prospective and randomized trial can answer the question," the researchers wrote, adding that the observed lower risk for Afib in vaccinated patients appears to support the hypothesis that influenza infection "is an important risk factor for AF."

In an editorial published with the study, researchers , and , of Northwestern University Feinberg School of Medicine in Chicago, wrote that despite its limitations, the study findings suggest that influenza infection may be a modifiable risk factor for Afib.

"Recently, a growing body of literature has examined this topic with several straightforward, yet promising, interventions identified," they wrote. "Weight loss, moderate exercise, and treatment for underlying obstructive sleep apnea (OSA) have all been shown to reduce the risk of AF incidence of recurrence. Influenza vaccination could represent another simple, cost-effective interventions to prevent AF."

They noted that it remains to be seen if treating existing influenza infection with viral neuraminidase-blocking drugs like Tamiflu, Relenza, and Inavir can reduce secondary Afib risk.

"The results of this study begs the question as to whether the acute treatment of the influenza infection itself with neuraminidase inhibitors or addressing the inflammatory response associated with infection may help prevent secondary episodes of AF," they wrote. "Beyond the prospective trial mentioned by the authors, we look forward to future studies into these and other areas that may help confirm and validate the observed findings."

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