Clinical Characteristics Are Similar across Type A and B Influenza Virus Infections.
BACKGROUND
Studies that aimed at comparing the clinical presentation of influenza patients across virus types and subtypes/lineages found divergent results, but this was never investigated using data collected over several years in a countrywide, primary care practitioners-based influenza surveillance system.


METHODS
The IBVD (Influenza B in Vircases Database) study collected information on signs and symptoms at disease onset from laboratory-confirmed influenza patients of any age who consulted a sentinel practitioner in France. We compared the clinical presentation of influenza patients across age groups (0-4, 5-14, 15-64 and 65+ years), virus types (A, B) and subtypes/lineages (A(H3N2), pandemic A(H1N1), B Victoria, B Yamagata).


RESULTS
Overall, 14,423 influenza cases (23.9% of which were influenza B) were included between 2003-2004 and 2012-2013. Influenza A and B accounted for over 50% of total influenza cases during eight and two seasons, respectively. There were minor differences in the distribution of signs and symptoms across influenza virus types and subtypes/lineages. Compared to patients aged 0-4 years, those aged 5-14 years were more likely to have been infected with type B viruses (OR 2.15, 95% CI 1.87-2.47) while those aged 15-64 years were less likely (OR 0.83, 95% CI 0.73-0.96). Males and influenza patients diagnosed during the epidemic period were less likely to be infected with type B viruses.


CONCLUSIONS
Despite differences in age distribution, the clinical illness produced by the different influenza virus types and subtypes is indistinguishable among patients that consult a general practitioner for acute respiratory infections.
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Anne
A
Mosnier
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Saverio
S
Caini
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Isabelle
I
Daviaud
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Elodie
E
Nauleau
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Tan Tai
TT
Bui
General Practitioner or Paediatrician, contributor of the GROG network, Paris, France.
Emmanuel
E
Debost
General Practitioner or Paediatrician, contributor of the GROG network, Paris, France.
Bernard
B
Bedouret
Laboratoire de Virologie, Centre Hospitalier Universitaire de Poitiers, Poitiers, France.
Gérard
G
Agius
Centre National de Référence des virus influenza, Génétique moléculaire des virus respiratoires, Institut Pasteur, CNRS UMR 3569, Université Paris Diderot Sorbonne Paris-Cité, Paris, France.
Sylvie
S
van der Werf
Centre National de Référence des virus influenza, CBPE, Hospices Civils de Lyon et Virpath, Université Claude Bernard Lyon, Lyon, France.
Bruno
B
Lina
Open Rome (Organize and Promote Epidemiological Network), Paris, France.
Jean Marie
JM
Cohen
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype; D053122:Influenza A Virus, H3N2 Subtype; D009980:Influenza A virus; D009981:Influenza B virus; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology / Q000473:pathology / Q000821:virology*; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D055815:Young Adult