Trends and disparities in breastfeeding initiation in France between 2010 and 2016: Results from the French National Perinatal Surveys.

Breastfeeding (BF) initiation rates in French maternity units are among the lowest in Europe. After increasing for several years, they decreased between 2010 and 2016, although several maternal characteristics known to be positively associated with BF in France were more frequent. We aimed to (1) quantify adjusted trends in BF initiation rates between 2010 and 2016; (2) examine associations between BF initiation rates and newborn, maternal, maternity unit, and department-level characteristics. Using data from the 2010 (n = 12,224) and 2016 (n = 11,089) French National Perinatal Surveys, we analysed BF initiation (exclusive, mixed, and any) through a succession of six mixed-effect multinomial regression models, progressively adding adjustment covariates. Adjusted exclusive and any BF initiation rates decreased by 9.6 and 4.5 points, respectively, versus by 7.7 and 1.8 points, respectively, in the crude analysis. In both years, adjusted exclusive and any BF initiation rates were lowest in the following categories of mothers: low education level, single, high body mass index and multiple or premature births. Exclusive BF initiation decreased most in primiparous mothers, those with the lowest household income, mothers that had a vaginal delivery, women born in an African country and those who delivered in a maternity unit without Baby-Friendly Hospital Initiative designation. The 2010-2016 decrease in BF initiation rates in France cannot be explained by changes in mothers' characteristics; quite the opposite, adjustment increased its magnitude. Additional efforts should be put in place to understand why this decrease is particularly sharp in some subgroups of mothers.

Noncompliance with blood donor selection criteria - Complidon 2017, France.

BACKGROUND: Blood donor selection, consisting of a pre-donation questionnaire and interview, excludes potential donors who may be at risk of transfusion-transmissible infections. Assessing the reasons for noncompliance with blood donor selection criteria is important to maintain a high level of viral safety of blood products. STUDY DESIGN AND METHODS: An anonymous French online survey of a sample of blood donors (Complidon) was conducted from September to December 2017. Data were poststratified to be representative of all donors who donated blood between July 2016 and December 2017. RESULTS: Of 420,190 solicited donors, 108,386 completed the survey (26%). Overall, noncompliance was estimated at 5.6%. The least respected criteria regarded sex with more than one partner during the previous 4 months for donors (1.9%) and for donors' partners (1%), travel-related criteria (1.2%) and sex between men during the previous 12 months (0.73% of men). Reasons for noncompliance differed according to criteria. Donors who were non-compliant to sexuality-based criteria mainly said they did not want to be excluded or that the questions were too personal. Conversely, donors who were exclusively non-compliant to criteria other than sexuality-based criteria more often mentioned their non-compliance during the pre-donation interview but were nevertheless authorized to donate blood. CONCLUSION: Despite noncompliance to blood donor criteria being relatively low in France, it still represents a threat to blood safety. Accordingly, improved communication is important to ensure that donors fully understand each selection criterion and to emphasize to health professionals the importance of listening carefully without judging during pre-donation interviews.

The evolving blood donor deferral policy for men who have sex with men: impact on the risk of HIV transmission by transfusion in France.

BACKGROUND: Blood donation deferral for men who have sex with men (MSM) in France was reduced from permanent to 12 months in July 2016. To inform a further reduction of the deferral period, an HIV risk assessment was conducted with two scenarios: S1, 4-month deferral; S2, 4-month deferral only in the case of more than one sexual partner (i.e., similar to other blood donors). METHODS: Baseline HIV residual risk (RR) was calculated from July 2016 to December 2017, using the Incidence Rate-Window Period method. The impact of both scenarios on RR was assessed using data from surveys on MSM and blood donors, to estimate 1) the number of additional MSM expected to donate in each scenario and 2) HIV incidence among these donors. RESULTS: Baseline HIV RR was estimated at 1 in 6,380,000 donations. For S1, an additional 733 MSM donors, and an additional 0.09 HIV-positive donations were estimated, yielding an unchanged RR of 1 in 6,300,000. For S2, these numbers were estimated at 3102 and 3.92, respectively, yielding an RR of 1 in 4,300,000. Sensitivity analyses showed that, under worst-case assumptions, the RR would equal 1 in 6,225,000 donations for S1 and 1 in 3,000,000 for S2. CONCLUSION: For both scenarios, the HIV RR remains very low. For S1, the risk is identical to the baseline RR. For S2, it is 1.5 times higher, and sensitivity analysis shows that this estimate is less robust than for S1. The French Minister of Health announced that S1 will be implemented in April 2020.

Noncompliance to blood donor selection criteria by men who have sex with men - Complidon 2017, France.

BACKGROUND AND OBJECTIVES: In France, blood donation deferral for men who have sex with men (MSM) was reduced from permanent to 12 months in July 2016. Assessing noncompliance (rate and reasons) with this criterion is important to maintain a high level of viral safety in blood products. MATERIALS AND METHODS: An anonymous online survey (Complidon) of a sample of blood donors was conducted in 2017. Data were post-stratified to be representative of all those who donated blood between July 2016 and December 2017. A multivariable analysis was performed to assess factors associated with noncompliance. RESULTS: Among male donors, 0·73% [95% CI: 0·63-0·83] reported having sex with men in the 12 months preceding their donation. Factors associated with noncompliance were as follows: young age, a low educational level, concerns about privacy, and better knowledge of donor selection criteria and the window period than compliant men. More than half of noncompliant MSM donors (57·6% [95% CI: 50·6-64·3]) felt that sexual orientation should not be a criterion for donation, 47·2% [95% CI: 40·4-54·0] did not disclose their male-to-male sexual relations in order to avoid being excluded from donating, 40·5% [95% CI: 34·0-47·4] reported using condoms and 21·8% [95% CI: 16·7-27·9] had the same male partner for at least 12 months. CONCLUSION: Complidon showed that compliance with blood donation criteria in MSM was high, but not optimal, especially among younger men. HIV residual risk did not increase after the implementation of 12-month deferral. Data from Complidon helped French policymakers to assess the additional HIV risk posed by increased access to blood donation for MSM.

Dengue serosurvey after a 2-month long outbreak in Nîmes, France, 2015: was there more than met the eye?

BackgroundClusters of dengue cases have recently become more frequent in areas of southern France colonised by the vector mosquito Aedes albopictus. In July 2015, a 2-month outbreak of dengue virus serotype 1 (DENV-1) was reported in Nîmes. Aim: We conducted a serosurvey in the affected area at the end of the vector activity period to determine the true extent of dengue transmission. Methods: We collected capillary blood from consenting household members, and information on their medical and travel histories, and exposure to mosquito bites. Recent infections were identified using IgM and IgG anti-DENV ELISA, followed, when positive, by plaque reduction neutralisation tests on serum against DENV 1-4 and West Nile virus. The prevalence estimator was calibrated on reference demographic data. We quantified the spatial clustering of dengue cases within the affected community and inferred the transmission tree. Results: The study participation rate was 39% (564/1,431). Three of 564 participants tested positive for DENV-1 infection (after marginal calibration, 0.41%; 95% confidence interval: 0.00-0.84). The spatial analysis showed that cases were clustered at the household level. Most participants perceived the presence of mosquitos as abundant (83%) and reported frequent mosquito bites (57%). We incidentally identified six past West Nile virus infections (0.9%; 95% CI: 0.2-1.6). Conclusion: This serosurvey confirms the potential for arboviral diseases to cause outbreaks - albeit limited for now - in France and Europe.

Improving regional influenza surveillance through a combination of automated outbreak detection methods: the 2015/16 season in France.

The 2014/15 influenza epidemic caused a work overload for healthcare facilities in France. The French national public health agency announced the start of the epidemic - based on indicators aggregated at the national level - too late for many hospitals to prepare. It was therefore decided to improve the influenza alert procedure through (i) the introduction of a pre-epidemic alert level to better anticipate future outbreaks, (ii) the regionalisation of surveillance so that healthcare structures can be informed of the arrival of epidemics in their region, (iii) the standardised use of data sources and statistical methods across regions. A web application was developed to deliver statistical results of three outbreak detection methods applied to three surveillance data sources: emergency departments, emergency general practitioners and sentinel general practitioners. This application was used throughout the 2015/16 influenza season by the epidemiologists of the headquarters and regional units of the French national public health agency. It allowed them to signal the first influenza epidemic alert in week 2016-W03, in Brittany, with 11 other regions in pre-epidemic alert. This application received positive feedback from users and was pivotal for coordinating surveillance across the agency's regional units.

Optimizing the precision of case fatality ratio estimates under the surveillance pyramid approach.

In the management of emerging infectious disease epidemics, precise and accurate estimation of severity indices, such as the probability of death after developing symptoms-the symptomatic case fatality ratio (sCFR)-is essential. Estimation of the sCFR may require merging data gathered through different surveillance systems and surveys. Since different surveillance strategies provide different levels of precision and accuracy, there is need for a theory to help investigators select the strategy that maximizes these properties. Here, we study the precision of sCFR estimators that combine data from several levels of the severity pyramid. We derive a formula for the standard error, which helps us find the estimator with the best precision given fixed resources. We further propose rules of thumb for guiding the choice of strategy: For example, should surveillance of a particular severity level be started? Which level should be preferred? We derive a formula for the optimal allocation of resources between chosen surveillance levels and provide a simple approximation that can be used in thinking more heuristically about planning surveillance. We illustrate these concepts with numerical examples corresponding to 3 influenza pandemic scenarios. Finally, we review the equally important issue of accuracy.

The impact of the Baby-Friendly Hospital Initiative on breastfeeding rates at maternity units in France.

BACKGROUND: The Baby-Friendly Hospital Initiative (BFHI) is associated with improved breastfeeding outcomes in many high-income countries including the UK and the USA, but its effectiveness has never been evaluated in France. We investigated the impact of the BFHI on breastfeeding rates in French maternity units in 2010, 2016 and 2021 to assess if the BFHI aids to reduce inequalities in breastfeeding. METHODS: We examined breastfeeding in maternity units (exclusive, mixed and any breastfeeding) in mothers of singleton full-term newborns using the 2010 (n = 13 075), 2016 (n = 10 919) and 2021 (n = 10 209) French National Perinatal Surveys. We used mixed-effect hierarchical multinomial regression models adjusting for neonatal, maternal, maternity unit and French administrative department characteristics, and tested certain interactions. RESULTS: The adjusted rate of exclusive breastfeeding was higher by +5.8 (3.4-8.1) points among mothers delivering in BFHI-accredited maternity units compared with those delivering in non-accredited units. When compared with average-weight newborns, this difference was sharper for infants with low birthweight: +14.9 (10.0-19.9) points when their birthweight was 2500 g. Mixed breastfeeding was lower by -1.7 points (-3.2-0) in BFHI-accredited hospitals, with no notable difference according to the neonatal or maternal characteristics. CONCLUSION: Mothers delivering in BFHI-accredited maternity units had higher exclusive breastfeeding rates and lower mixed breastfeeding rates than those delivering in non-accredited maternity units. The positive impact of the BFHI was stronger among low-birthweight neonates, who are less often breastfed, helping reduce the gap for this vulnerable group while favouring mothers with higher education levels.

Planning for the next influenza H1N1 season: a modelling study.

BACKGROUND: The level of herd immunity before and after the first 2009 pandemic season is not precisely known, and predicting the shape of the next pandemic H1N1 season is a difficult challenge. METHODS: This was a modelling study based on data on medical visits for influenza-like illness collected by the French General Practitioner Sentinel network, as well as pandemic H1N1 vaccination coverage rates, and an individual-centred model devoted to influenza. We estimated infection attack rates during the first 2009 pandemic H1N1 season in France, and the rates of pre- and post-exposure immunity. We then simulated various scenarios in which a pandemic influenza H1N1 virus would be reintroduced into a population with varying levels of protective cross-immunity, and considered the impact of extending influenza vaccination. RESULTS: During the first pandemic season in France, the proportion of infected persons was 18.1% overall, 38.3% among children, 14.8% among younger adults and 1.6% among the elderly. The rates of pre-exposure immunity required to fit data collected during the first pandemic season were 36% in younger adults and 85% in the elderly. We estimated that the rate of post-exposure immunity was 57.3% (95% Confidence Interval (95%CI) 49.6%-65.0%) overall, 44.6% (95%CI 35.5%-53.6%) in children, 53.8% (95%CI 44.5%-63.1%) in younger adults, and 87.4% (95%CI 82.0%-92.8%) in the elderly.The shape of a second season would depend on the degree of persistent protective cross-immunity to descendants of the 2009 H1N1 viruses. A cross-protection rate of 70% would imply that only a small proportion of the population would be affected. With a cross-protection rate of 50%, the second season would have a disease burden similar to the first, while vaccination of 50% of the entire population, in addition to the population vaccinated during the first pandemic season, would halve this burden. With a cross-protection rate of 30%, the second season could be more substantial, and vaccination would not provide a significant benefit. CONCLUSIONS: These model-based findings should help to prepare for a second pandemic season, and highlight the need for studies of the different components of immune protection.

A method for selecting and monitoring medication sales for surveillance of gastroenteritis.

PURPOSE: Monitoring appropriate categories of medication sales can provide early warning of certain disease outbreaks. This paper presents a methodology for choosing and monitoring medication sales relevant for the surveillance of gastroenteritis and assesses the operational characteristics of the selected medications for early warning. METHODS: Acute diarrhoea incidences in mainland France were obtained from the Sentinelles network surveillance system for the period 2000-2009. Medication sales grouped by therapeutic classes were obtained on the same period. Hierarchical clustering was used to select therapeutic classes correlating with disease incidence over the period. Alert thresholds were defined for the selected therapeutic classes. Single and multiple voter algorithms were investigated for outbreak detection based on sales crossing the thresholds. Sensitivity and specificity were calculated respective to known outbreaks periods. RESULTS: Four therapeutic classes were found to cluster with acute diarrhoea incidence. The therapeutic class other antiemetic and antinauseants had the best sensitivity (100%) and timeliness (1.625 weeks before official alerts), for a false alarm rate of 5%. Multiple voter algorithm was the most efficient with the rule: 'Emit an outbreak alert when at least three therapeutic classes are over their threshold' (sensitivity 100%, specificity 95%, timeliness 1.750 weeks before official alerts). CONCLUSIONS: The presented method allowed selection of relevant therapeutic classes for surveillance of a specific condition. Multiple voter algorithm based on several therapeutic classes performed slightly better than the best therapeutic class alone, while improving robustness against abrupt changes occurring in a single therapeutic class.

Short-term effects of airborne pollens on asthma attacks as seen by general practitioners in the Greater Paris area, 2003-2007.

AIMS: To investigate for the first time the short-term effects of airborne pollen counts on general practitioner (GP) consultations for asthma attacks in the Greater Paris area between 2003-2007. METHODS: Counts were available for common pollens (Betula, Cupressa, Fraxinus and Poaceae). Weekly data on GP visits for asthma attacks were obtained from the French GP Sentinel Network. A quasi-Poisson regression with generalised additive models was implemented. Short-term effects of pollen counts were assessed using single and multi-pollen models after adjustment for air pollution and influenza. RESULTS: A mean weekly incidence rate of 25.4 cases of asthma attacks per 100,000 inhabitants was estimated during the study period. The strongest significant association between asthma attacks and pollen counts was registered for grass (Poaceae) in the same week of asthma attacks, with a slight reduction of the effect observed in the multi-pollen model. Adjusted relative risk for Poaceae was 1.54 (95% CI: 1.33-1.79) with an inter-quartile range increase of 17.6 grains/m3 during the pollen season. CONCLUSIONS: For the first time, a significant short-term association was observed between Poaceae pollen counts and consultations for asthma attacks as seen by GPs. These findings need to be confirmed by more consistent time-series and investigations on a daily basis.

Mapping influenza activity in emergency departments in France using Bayesian model-based geostatistics.

BACKGROUND: Maps of influenza activity are important tools to monitor influenza epidemics and inform policymakers. In France, the availability of a high-quality data set from the Oscour® surveillance network, covering 92% of hospital emergency department (ED) visits, offers new opportunities for disease mapping. Traditional geostatistical mapping methods such as Kriging ignore underlying population sizes, are not suited to non-Gaussian data and do not account for uncertainty in parameter estimates. OBJECTIVE: Our objective was to create reliable weekly interpolated maps of influenza activity in the ED setting, to inform Santé publique France (the French national public health agency) and local healthcare authorities. METHODS: We used Oscour® data of ED visits covering the 2016-2017 influenza season. We developed a Bayesian model-based geostatistical approach, a class of generalized linear mixed models, with a multivariate normal random field as a spatially autocorrelated random effect. Using R-INLA, we developed an algorithm to create maps of the proportion of influenza-coded cases among all coded visits. We compared our results with maps obtained by Kriging. RESULTS: Over the study period, 45 565 (0.82%) visits were coded as influenza cases. Maps resulting from the model are presented for each week, displaying the posterior mean of the influenza proportion and its associated uncertainty. Our model performed better than Kriging. CONCLUSIONS: Our model allows producing smoothed maps where the random noise has been properly removed to reveal the spatial risk surface. The algorithm was incorporated into the national surveillance system to produce maps in real time and could be applied to other diseases.

Online detection and quantification of epidemics.

BACKGROUND: Time series data are increasingly available in health care, especially for the purpose of disease surveillance. The analysis of such data has long used periodic regression models to detect outbreaks and estimate epidemic burdens. However, implementation of the method may be difficult due to lack of statistical expertise. No dedicated tool is available to perform and guide analyses. RESULTS: We developed an online computer application allowing analysis of epidemiologic time series. The system is available online at http://www.u707.jussieu.fr/periodic_regression/. The data is assumed to consist of a periodic baseline level and irregularly occurring epidemics. The program allows estimating the periodic baseline level and associated upper forecast limit. The latter defines a threshold for epidemic detection. The burden of an epidemic is defined as the cumulated signal in excess of the baseline estimate. The user is guided through the necessary choices for analysis. We illustrate the usage of the online epidemic analysis tool with two examples: the retrospective detection and quantification of excess pneumonia and influenza (P&I) mortality, and the prospective surveillance of gastrointestinal disease (diarrhoea). CONCLUSION: The online application allows easy detection of special events in an epidemiologic time series and quantification of excess mortality/morbidity as a change from baseline. It should be a valuable tool for field and public health practitioners.

Universal or targeted approach to prevent the transmission of extended-spectrum beta-lactamase-producing Enterobacteriaceae in intensive care units: a cost-effectiveness analysis.

OBJECTIVE: Several control strategies have been used to limit the transmission of multidrug-resistant organisms in hospitals. However, their implementation is expensive and effectiveness of interventions for the control of extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-PE) spread is controversial. Here, we aim to assess the cost-effectiveness of hospital-based strategies to prevent ESBL-PE transmission and infections. DESIGN: Cost-effectiveness analysis based on dynamic, stochastic transmission model over a 1-year time horizon. PATIENTS AND SETTING: Patients hospitalised in a hypothetical 10-bed intensive care unit (ICU) in a high-income country. INTERVENTIONS: Base case scenario compared with (1) universal strategies (eg, improvement of hand hygiene (HH) among healthcare workers, antibiotic stewardship), (2) targeted strategies (eg, screening of patient for ESBL-PE at ICU admission and contact precautions or cohorting of carriers) and (3) mixed strategies (eg, targeted approaches combined with antibiotic stewardship). MAIN OUTCOMES AND MEASURES: Cases of ESBL-PE transmission, infections, cost of intervention, cost of infections, incremental cost per infection avoided. RESULTS: In the base case scenario, 15 transmissions and five infections due to ESBL-PE occurred per 100 ICU admissions, representing a mean cost of €94 792. All control strategies improved health outcomes and reduced costs associated with ESBL-PE infections. The overall costs (cost of intervention and infections) were the lowest for HH compliance improvement from 55%/60% before/after contact with a patient to 80%/80%. CONCLUSIONS: Improved compliance with HH was the most cost-saving strategy to prevent the transmission of ESBL-PE. Antibiotic stewardship was not cost-effective. However, adding antibiotic restriction strategy to HH or screening and cohorting strategies slightly improved their effectiveness and may be worthy of consideration by decision-makers.

Hand Hygiene, Cohorting, or Antibiotic Restriction to Control Outbreaks of Multidrug-Resistant Enterobacteriaceae.

BACKGROUND: The best strategy for controlling extended-spectrum ß-lactamase-producing Enterobacteriaceae (ESBL-PE) transmission in intensive care units (ICUs) remains elusive. OBJECTIVE: We developed a stochastic transmission model to quantify the effectiveness of interventions aimed at reducing the spread of ESBL-PE in an ICU. METHODS: We modeled the evolution of an outbreak caused by the admission of a single carrier in a 10-bed ICU free of ESBL-PE. Using data obtained from recent muticenter studies, we studied 26 strategies combining different levels of the following 3 interventions: (1) increasing healthcare worker compliance with hand hygiene before and after contact with a patient; (2) cohorting; (3) reducing antibiotic prevalence at admission with or without reducing antibiotherapy duration. RESULTS: Improving hand hygiene compliance from 55% before patient contact and 60% after patient contact to 80% before and 80% after patient contact reduced the nosocomial incidence rate of ESBL-PE colonization by 91% at 90 days. Adding cohorting to hand hygiene improvement intervention decreased the proportion of ESBL-PE acquisitions by an additional 7%. Antibiotic restriction had the lowest impact on the epidemic. When combined with other interventions, it only marginally improved effectiveness, despite strong hypotheses regarding antibiotic impact on transmission. CONCLUSION: Our results suggest that hand hygiene is the most effective intervention to control ESBL-PE transmission in an ICU.

Costs associated with implementation of a strict policy for controlling spread of highly resistant microorganisms in France.

OBJECTIVE: To assess costs associated with implementation of a strict 'search and isolate' strategy for controlling highly drug-resistant organisms (HDRO). DESIGN: Review of data from 2-year prospective surveillance (01/2012 to 12/2013) of HDRO. SETTING: Three university hospitals located in northern Paris. METHODS: Episodes were defined as single cases or outbreaks of glycopeptide-resistant enterococci (GRE) or carbapenemase-producing Enterobacteriacae (CPE) colonisation. Costs were related to staff reinforcement, costs of screening cultures, contact precautions and interruption of new admissions. Univariate analysis, along with simple and multiple linear regression analyses, was conducted to determine variables associated with cost of HDRO management. RESULTS: Overall, 41 consecutive episodes were included, 28 single cases and 13 outbreaks. The cost (mean ± SD) associated with management of a single case identified within and/or 48 h after admission was €4443 ± 11,552 and €11,445 ± 15,743, respectively (p<0.01). In an outbreak, the total cost varied from €14,864 ± 17,734 for an episode with one secondary case (€7432 ± 8867 per case) to €136,525 ± 151,231 (€12,845 ± 5129 per case) when more than one secondary case occurred. In episodes of single cases, contact precautions and microbiological analyses represented 51% and 30% of overall cost, respectively. In outbreaks, cost related to interruption of new admissions represented 77-94% of total costs, and had the greatest financial impact (R(2)=0.98, p<0.01). CONCLUSIONS: In HDRO episodes occurring at three university hospitals, interruption of new admissions constituted the most costly measure in an outbreak situation.

Hospitalization of influenza-like illness patients recommended by general practitioners in France between 1997 and 2010.

BACKGROUND: The case-hospitalization ratio (CHR) is a key quantity for the management of emerging pathogens such as pandemic influenza. Yet, few running surveillance systems prospectively monitor the CHR during influenza epidemics. Here, we analyze the proportion of recommended hospitalizations (PRH) among influenza-like illness (ILI) patients attended in general practice in France and compare the PRH observed during the 2009-2010 A(H1N1) pandemic with the one of the twelve previous seasons. METHODS: ILI cases were recorded by general practitioners (GPs) involved in surveillance, who indicated for each case whether they recommended hospitalization. We stratify the analysis by age, sex, and viral subtype. We investigate the reasons why GPs recommended hospitalization and the presence of risk factors for pandemic A(H1N1) complications. RESULTS: The average PRH over the seasons 1997-1998 to 2008-2009 was 3·4‰ (3-3·9). It was three times higher during the 2009-2010 pandemic than during seasonal influenza epidemics (OR = 2·89, 95% CI: 2·28-3·64). The highest increase was among 20-39-year-old women: OR = 11·8 (5·04-29·59). Overall, the principal reasons for recommending hospitalization were "respiratory problems" and "bad general condition." However, during the pandemic, "age" (mainly associated with infants), "pregnancy," and "diagnostic" became more frequent than before (P < 0·001). Finally, pregnancy was the reported risk factor for pandemic A(H1N1) complications that had the largest impact on hospitalization recommendation during the pandemic (OR = 38·62, P < 0·001). CONCLUSION: Easily implemented in surveillance systems, this protocol has the potential to reveal changes in hospitalization recommendation by GPs. Moreover, if the right data are collected alongside, it could give timely insights into epidemic severity.

Age distribution of influenza like illness cases during post-pandemic A(H3N2): comparison with the twelve previous seasons, in France.

In France, the 2011-2012 influenza epidemic was characterized by the circulation of antigenically drifted influenza A(H3N2) viruses and by an increased disease severity and mortality among the elderly, with respect to the A(H1N1)pdm09 pandemic and post-pandemic outbreaks. Whether the epidemiology of influenza in France differed between the 2011-2012 epidemic and the previous outbreaks is unclear. Here, we analyse the age distribution of influenza like illness (ILI) cases attended in general practice during the 2011-2012 epidemic, and compare it with that of the twelve previous epidemic seasons. Influenza like illness data were obtained through a nationwide surveillance system based on sentinel general practitioners. Vaccine effectiveness was also estimated. The estimated number of ILI cases attended in general practice during the 2011-2012 was lower than that of the past twelve epidemics. The age distribution was characteristic of previous A(H3N2)-dominated outbreaks: school-age children were relatively spared compared to epidemics (co-)dominated by A(H1N1) and/or B viruses (including the 2009 pandemic and post-pandemic outbreaks), while the proportion of adults over 30 year-old was higher. The estimated vaccine effectiveness (54%, 95% CI (48, 60)) was in the lower range for A(H3N2) epidemics. In conclusion, the age distribution of ILI cases attended in general practice seems to be not different between the A(H3N2) pre-pandemic and post-pandemic epidemics. Future researches including a more important number of ILI epidemics and confirmed virological data of influenza and other respiratory pathogens are necessary to confirm these results.