Flu may trigger systemic lupus erythematosus flares

Influenza infection appears to be a risk factor for systemic lupus erythematosus (SLE) flares needing hospitalization, independently of patient age, sex, and comorbidities, a recent study has found.

Drawing from the national healthcare insurance database of Korea, the researchers identified 1,455 SLE patients between 2014 and 2018. Participants were set as their own controls, with the risk interval defined as the first 7 days after index influenza data, and control interval as all other times in each year. Flares were compared between risk and control periods.

Overall, 1,624 influenza infections were documented, and 79 SLE patients (mean age, 35.7±14.9 years; 86.1 percent female) saw a total of 98 flares. Flares were significantly more likely to occur during the first 7 days after index infection vs any other observation period (incidence ratio, 25.75, 95 percent confidence interval [CI], 17.63–37.59).

Further stratification showed that such an effect of influenza on SLE was much stronger during the first 3 days of infection (incidence ratio, 21.81, 95 percent CI, 14.71–32.35) than on the fourth to seventh days (incidence ratio, 7.56, 95 percent CI, 3.69–15.47).

Subgroup and sensitivity analyses—looking for differential effects according to sex and age, duration of washout period, varying control intervals, and definitions of SLE and influenza—did not meaningfully alter the primary findings.

“Possibility of increased risk for SLE flares resulting in hospitalization within seven days after influenza infection has to be considered when treating and educating patients with SLE,” the researchers said.