Pandemic influenza A (H1N1) 2009: chest radiographic findings from 147 proven cases in the Montreal area.
OBJECTIVE
To describe chest radiographic findings in patients with isolated and complicated acute novel influenza A (H1N1) virus infection.


METHODS
Retrospective study of 147 patients (64 men, mean age 41) with reverse-transcriptase polymerase chain reaction confirmed acute influenza A (H1N1) infection, who also had a chest radiograph <72 hours of viral specimen collection. Radiographs were analysed for acute findings. A correlation with bacterial cultures results was performed. The unpaired 2-sample equal-variance Student t test was applied to continuous variables and the Pearson χ(2) test of association to discrete variables.


RESULTS
In 71% of cases, chest radiograph was normal. The presence of acute imaging findings was associated with older age (P < .05), increased number of comorbidities (most commonly, chronic obstructive pulmonary disease, diabetes, asthma) (P < .05), higher rate of hospitalization (P < .05) and intensive care unit admission, and increased mortality. Predominant acute radiographic finding in isolated influenza A (H1N1) was alveolar opacity (88%), either unifocal or multifocal, most often in the lower lobes. In the subgroup of patients with positive imaging findings and for whom nonviral microbiologic data was available, 62% had superimposed bacterial or fungal infection.


CONCLUSIONS
In the majority of patients with acute influenza A (H1N1) infection, the chest radiograph is normal. Acute imaging findings are associated with older age, an increased number of comorbidities, and a higher rate of complications and mortality. The predominant radiographic finding of isolated primary influenza A (H1N1) infection is alveolar opacity. Superimposed bacterial infection is frequent and must be excluded in patients with abnormal imaging.
Radiology Department, University of Montreal Medical Center (CHUM), Montreal, Québec, Canada.
Alexandre
A
Semionov
Cécile
C
Tremblay
Louise
L
Samson
Martin
M
Chandonnet
Jean
J
Chalaoui
Carl
C
Chartrand-Lefebvre
D000328:Adult; D017677:Age Distribution; D001249:Asthma / Q000000981:diagnostic imaging / Q000453:epidemiology; D015897:Comorbidity; D003920:Diabetes Mellitus / Q000453:epidemiology; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D009980:Influenza A virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000821:virology; D008168:Lung / Q000000981:diagnostic imaging*; D008297:Male; D015588:Observer Variation; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011792:Quebec / Q000453:epidemiology; D011859:Radiography; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods