Influenza infection and risk of acute pulmonary embolism.
BACKGROUND
Influenza infections have been associated with procoagulant changes. Whether influenza infections lead to an increased risk of pulmonary embolism remains to be established.


METHODS
We conducted a nested case control study in a large cohort of patients with a clinical suspicion of having pulmonary embolism. Blood samples were collected to investigate the presence of influenza A and B by complement fixation assay (CFA). We compared case patients, in whom pulmonary embolism was proven (n = 102), to controls, in whom pulmonary embolism was excluded (n = 395). Furthermore, we compared symptoms of influenza-like illness in both patient groups 2 weeks prior to inclusion in the study, using the influenza-like illness (ILI) score, which is based on a questionnaire. We calculated the risk of pulmonary embolism associated with influenza infection.


RESULTS
The percentage of patients with influenza A was higher in the control group compared to the case group (4.3% versus 1.0%, respectively, odds ratio 0.22; 95% CI: 0.03-1.72). Influenza B was not detectable in any of the cases and was found in 3 of the 395 controls (0.8%). The ILI score was positive in 24% of the cases and 25% in the control persons (odds ratio 1.16, 95% CI: 0.67-2.01). We did not observe an association between the ILI score and proven influenza infection.


CONCLUSIONS
In this clinical study, influenza infection was not associated with an increased risk of acute pulmonary embolism. The ILI score is non-specific in this clinical setting.
van Wissen
Matthijs
M
Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands. Matthijs.vanWissen@slz.nl.
Keller
Tymen T
TT
Ronkes
Brechje
B
Gerdes
Victor Ea
VE
Zaaijer
Hans L
HL
van Gorp
Eric Cm
EC
Brandjes
Dees Pm
DP
Levi
Marcel
M
Büller
Harry R
HR