Additional file 2: Table S1. of Ten influenza seasons in France: distribution and timing of influenza A and B circulation, 2003–2013

Weekly average (and median) of the estimated incidence (per 100,000 inhabitants) of medically-attended influenza. Data were only shown for virus type and subtypes that accounted for at least 1 % of all influenza cases in that season. Source: GROG influenza sentinel surveillance network, France, 2003–2004 to 2012–2013. (DOC 31 kb

Additional file 1: of Ten influenza seasons in France: distribution and timing of influenza A and B circulation, 2003–2013

GROG network. ARI and influenza incidence estimation. (DOC 92 kb

Clinical Presentation of Influenza B Patients According to Age Group and Virus Lineage (Victoria versus Yamagata).

<p>^a Sudden onset of symptoms is not presented as included in the ARI case definition; dyspnoea is not presented as only collected since the 2009–2010 season.</p><p>p-value for the comparison with influenza B patients of the same age group:</p><p>* <0.05</p><p>**<0.01</p><p>The IBVD (Influenza B in Vircases database) Study, France, 2003–2004 to 2012–2013.</p

Clinical Characteristics Are Similar across Type A and B Influenza Virus Infections

<div><p>Background</p><p>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.</p><p>Methods</p><p>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).</p><p>Results</p><p>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.</p><p>Conclusions</p><p>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.</p></div

Age distribution of influenza cases by virus type and subtype.

<p>The IBVD (Influenza B in Vircases database) study, France, 2003–2004 to 2012–2013. The age distribution of H3N2 cases is shown in red, B cases in grey and H1pdm09 in blue.</p

Variables associated with the odds of having been infected with influenza type B vs. A viruses.

<p>^a Signs and symptoms included were as follows: sudden onset of symptoms, asthenia, myalgia, shivering, cephalalgia, cough, expectoration, bronchitis/bronchiolitis, rhinitis, pharyngitis, otitis/earache, gastrointestinal symptoms, dyspnea, conjunctivitis, adenopathy.</p><p>Multivariable logistic regression analysis adjusted by season. The IBVD (Influenza B in Vircases database) study, France, 2003–2004 to 2012–2013.</p

Number of consultations with practitioners of patients infected with influenza B and A, by age groups.

<p>France and Turkey, 2010–2012.</p

Flow chart of the influenza A and B patients included in the IBVD (Influenza B in Vircases Database) study.

<p>Flow chart of the influenza A and B patients included in the IBVD (Influenza B in Vircases Database) study.</p

Questionnaire for data collection at days 9 and 28 in the IBGP study.

<p>France and Turkey, 2010–2012.</p

Epidemic peak and type, subtype and lineage of influenza cases detected within the French and Turkish influenza surveillance networks during 2010–2011 and 2011–2012 seasons, and (within parenthesis, in bold) included in the IBGP study.

<p>Epidemic peak and type, subtype and lineage of influenza cases detected within the French and Turkish influenza surveillance networks during 2010–2011 and 2011–2012 seasons, and (within parenthesis, in bold) included in the IBGP study.</p