Influenza surveillance: experiences from establishing a sentinel surveillance system in Germany

An Old Acquaintance: Could Adenoviruses Be Our Next Pandemic Threat?

Human adenoviruses (HAdV) are one of the most important pathogens detected in acute respiratory diseases in pediatrics and immunocompromised patients. In 1953, Wallace Rowe described it for the first time in oropharyngeal lymphatic tissue. To date, more than 110 types of HAdV have been described, with different cellular tropisms. They can cause respiratory and gastrointestinal symptoms, even urinary tract inflammation, although most infections are asymptomatic. However, there is a population at risk that can develop serious and even lethal conditions. These viruses have a double-stranded DNA genome, 25-48 kbp, 90 nm in diameter, without a mantle, are stable in the environment, and resistant to fat-soluble detergents. Currently the diagnosis is made with lateral flow immunochromatography or molecular biology through a polymerase chain reaction. This review aimed to highlight the HAdV variability and the pandemic potential that a HAdV3 and 7 recombinant could have considering the aggressive outbreaks produced in health facilities. Herein, we described the characteristics of HAdV, from the infection to treatment, vaccine development, and the evaluation of the social determinants of health associated with HAdV, suggesting the necessary measures for future sanitary control to prevent disasters such as the SARS-CoV-2 pandemic, with an emphasis on the use of recombinant AdV vaccines to control other potential pandemics.

The Sentiworld project: global mapping of sentinel surveillance networks in general practice

BACKGROUND

Sentinel networks composed of general practitioners (GPs) represent a powerful tool for epidemiologic surveillance and ad-hoc studies. Globalization necesitates greater international cooperation among sentinel networks. The aim of this study was to inventory GP sentinel networks involved in epidemiological surveillance on a global scale.

METHODS

GP sentinel surveillance networks were inventoried globally between July 2016 and December 2019. Each identified network was required to fill out an electronic descriptive survey for inclusion.

RESULTS

A total of 148 networks were identified as potential surveillance networks in general practice and were contacted. Among them, 48 were included in the study. Geographically, 33 networks (68.8%) were located in Europe and 38 (79.2%) had national coverage. The number of GPs registered in these networks represented between 0.1 and 100% of the total number of GPs in the network's country or region, with a median of 2.5%. All networks were involved in continuous epidemiologic surveillance and 47 (97.9%) monitored influenza-like illness. Data collection methods were paper-based forms (n = 26, 55.3%), electronic forms on a dedicated website (n = 18, 38.3%), electronic forms on a dedicated software program (n = 14, 29.8%), and direct extraction from electronic medical records (n = 14, 29.8%). Along with this study, a website has been created to share all data collected.

CONCLUSIONS

This study represents the first global geographic mapping of GP sentinel surveillance networks. By sharing this information, collaboration between networks will be easier, which can strengthen the quality of international epidemiologic surveillance. In the face of crises like that of COVID-19, this is more imperative than ever before.

[Monitoring of COVID-19 by extending existing surveillance for acute respiratory infections]

Im Rahmen der nationalen Influenzapandemieplanung wurden in Deutschland neben dem Meldewesen gemäß Infektionsschutzgesetz (IfSG) weitere Überwachungssysteme etabliert. Ziel dieser Systeme sind die Beschreibung, Analyse und Bewertung der Situation bei akuten respiratorischen Erkrankungen (ARE), die Identifikation der hauptsächlich zirkulierenden Atemwegserreger und die Beschreibung des zeitlichen Verlaufs. Seit Beginn der COVID-19-Pandemie wurden die Systeme erweitert, um auch Infektionen mit SARS-CoV‑2 erfassen zu können.

In diesem Beitrag werden drei verschiedene Surveillance-Systeme für ARE vorgestellt: GrippeWeb, die Arbeitsgemeinschaft Influenza mit dem SEED^ARE-Modul (Sentinel zur elektronischen Erfassung von Diagnosecodes) und das Krankenhaus-Sentinel ICOSARI (ICD-10-code-basierte Krankenhaus-Surveillance schwerer akuter respiratorischer Infektionen). Mit diesen Systemen können ARE auf Bevölkerungsebene, im ambulanten und im stationären Bereich überwacht werden. Zusammen mit dem Monitoring der Mortalität liefern sie wichtige Hinweise zur Häufigkeit verschieden schwerer Krankheitsverläufe in der Bevölkerung. Um die Systeme für SARS-CoV‑2 zu erweitern, waren nur wenige Anpassungen notwendig.

Da die Falldefinitionen für ARE nicht geändert wurden, können in den beschriebenen Systemen historische Zeitreihen zum Vergleich herangezogen werden. Alle Systeme sind so aufgebaut, dass stabile und etablierte Bezugsgrößen für die Berechnung von wöchentlichen Anteilen und Raten zur Verfügung stehen. Dies ist eine wichtige Ergänzung zum Meldewesen gemäß IfSG, welches stark von Testkapazitäten und -strategien sowie veränderten Falldefinitionen abhängt. Die Surveillance-Systeme haben sich in der COVID-19-Pandemie auch im internationalen Vergleich als praktikabel und effizient erwiesen.

Empowering primary healthcare institutions against COVID-19 pandemic: A health system-based approach

Primary health care institutions (PHCIs) are an essential foundation for the national response to COVID-19 disease in India. With the soaring number of confirmed cases, the health system is currently under unprecedented stress. In this scenario, there is a pressing need for empowering PHCIs in COVID-19 preparedness and response. The World Health Organization's (WHO) "Health system building block" approach is a classic model, which can work as a road map for the national health system in the process of empowering PHCIs against COVID-19 as well as other upcoming global and regional public health emergencies.

Establishing an ICD-10 code based SARI-surveillance in Germany - description of the system and first results from five recent influenza seasons

BACKGROUND

Syndromic surveillance of severe acute respiratory infections (SARI) is important to assess seriousness of disease as recommended by WHO for influenza. In 2015 the Robert Koch Institute (RKI) started to collaborate with a private hospital network to develop a SARI surveillance system using case-based data on ICD-10 codes. This first-time description of the system shows its application to the analysis of five influenza seasons.

METHODS

Since week 40/2015, weekly updated anonymized data on discharged patients overall and on patients with respiratory illness including ICD-10 codes of primary and secondary diagnoses are transferred from the network data center to RKI. Retrospective datasets were also provided. Our descriptive analysis is based on data of 47 sentinel hospitals collected between weeks 1/2012 to 20/2016. We applied three different SARI case definitions (CD) based on ICD-10 codes for discharge diagnoses of respiratory tract infections (J09 - J22): basic CD (BCD), using only primary diagnoses; sensitive CD (SCD), using primary and secondary diagnoses; timely CD (TCD), using only primary diagnoses of patients hospitalized up to one week. We compared the CD with regard to severity, age distribution and timeliness and with results from the national primary care sentinel system.

RESULTS

The 47 sentinel hospitals covered 3.6% of patients discharged from all German hospitals in 2013. The SCD comprised 2.2 times patients as the BCD, and 3.6 times as many as the TCD. Time course of SARI cases corresponded well to results from primary care surveillance and influenza virus circulation. The patients fulfilling the TCD had been completely reported after 3 weeks, which was fastest among the CD. The proportion of SARI cases among patients was highest in the youngest age group of below 5-year-olds. However, the age group 60 years and above contributed most SARI cases. This was irrespective of the CD used.

CONCLUSIONS

In general, available data and the implemented reporting system are appropriate to provide timely and reliable information on SARI in inpatients in Germany. Our ICD-10-based approach proved to be useful for fulfilling requirements for SARI surveillance. The exploratory approach gave valuable insights in data structure and emphasized the advantages of different CD.

Evolution of the hemagglutinin expressed by human influenza A(H1N1)pdm09 and A(H3N2) viruses circulating between 2008-2009 and 2013-2014 in Germany

This report describes the evolution of the influenza A(H1N1)pdm09 and A(H3N2) viruses circulating in Germany between 2008-2009 and 2013-2014. The phylogenetic analysis of the hemagglutinin (HA) genes of both subtypes revealed similar evolution of the HA variants that were also seen worldwide with minor exceptions. The analysis showed seven distinct HA clades for A(H1N1)pdm09 and six HA clades for A(H3N2) viruses. Herald strains of both subtypes appeared sporadically since 2008-2009. Regarding A(H1N1)pdm09, herald strains of HA clade 3 and 4 were detected late in the 2009-2010 season. With respect to A(H3N2), we found herald strains of HA clade 3, 4 and 7 between 2009 and 2012. Those herald strains were predominantly seen for minor and not for major HA clades. Generally, amino acid substitutions were most frequently found in the globular domain, including substitutions near the antigenic sites or the receptor binding site. Differences between both influenza A subtypes were seen with respect to the position of the indicated substitutions in the HA. For A(H1N1)pdm09 viruses, we found more substitutions in the stem region than in the antigenic sites. In contrast, in A(H3N2) viruses most changes were identified in the major antigenic sites and five changes of potential glycosylation sites were identified in the head of the HA monomer. Interestingly, we found in seasons with less influenza activity a relatively high increase of substitutions in the head of the HA in both subtypes. This might be explained by the fact that mutations under negative selection are subsequently compensated by secondary mutations to restore important functions e.g. receptor binding properties. A better knowledge of basic evolution strategies of influenza viruses will contribute to the refinement of predictive mathematical models for identifying novel antigenic drift variants.

Global monitoring of influenza: potential contribution of national networks from a French perspective

The aim of global monitoring of influenza is to help decision making in regular seasonal influenza and in the case of a new pandemic. FluNet is the main tool for information sharing among the WHO Global Influenza Surveillance Network, as well as the public. It allows 112 WHO National Influenza Centers in 83 countries access to remote data entry. Weekly information on recent isolates and epidemiological situations are available to the public through many functionalities, for example, maps (animated or static), charts and raw data are embedded in the system for data display. Thus far, FluNet has collected weekly influenza surveillance data from up to 1997. A major outcome of this global network is the influenza vaccine composition, which is proposed twice a year (i.e., for both hemispheres) on the basis of the collected data. However, FluNet is far from performing comprehensive monitoring of influenza at a global level; 109 WHO member states still do not participate in the network and participating national influenza centers have only limited resources, which do not allow them to implement a reliable, accurate and real-time epidemiology of influenza in the areas they deserve. By following the time and space dynamics of an influenza strain, an epidemiologically valid system would make assessment of decisions after adopting preventive measures (e.g., closing schools, travel restriction, use of antivirals or of protective masks and mass immunization) possible. This international cooperation in public health fields must be considerably reinforced in the future, and should encourage database linkage with environmental information, allowing for the evaluation of the role of climate change, animal behavior or pollution involvement in disease.

Physician privacy concerns when disclosing patient data for public health purposes during a pandemic influenza outbreak

Background

Privacy concerns by providers have been a barrier to disclosing patient information for public health purposes. This is the case even for mandated notifiable disease reporting. In the context of a pandemic it has been argued that the public good should supersede an individual's right to privacy. The precise nature of these provider privacy concerns, and whether they are diluted in the context of a pandemic are not known. Our objective was to understand the privacy barriers which could potentially influence family physicians' reporting of patient-level surveillance data to public health agencies during the Fall 2009 pandemic H1N1 influenza outbreak.

Methods

Thirty seven family doctors participated in a series of five focus groups between October 29-31 2009. They also completed a survey about the data they were willing to disclose to public health units. Descriptive statistics were used to summarize the amount of patient detail the participants were willing to disclose, factors that would facilitate data disclosure, and the consensus on those factors. The analysis of the qualitative data was based on grounded theory.

Results

The family doctors were reluctant to disclose patient data to public health units. This was due to concerns about the extent to which public health agencies are dependable to protect health information (trusting beliefs), and the possibility of loss due to disclosing health information (risk beliefs). We identified six specific actions that public health units can take which would affect these beliefs, and potentially increase the willingness to disclose patient information for public health purposes.

Conclusions

The uncertainty surrounding a pandemic of a new strain of influenza has not changed the privacy concerns of physicians about disclosing patient data. It is important to address these concerns to ensure reliable reporting during future outbreaks.

A secure protocol for protecting the identity of providers when disclosing data for disease surveillance

BACKGROUND

Providers have been reluctant to disclose patient data for public-health purposes. Even if patient privacy is ensured, the desire to protect provider confidentiality has been an important driver of this reluctance.

METHODS

Six requirements for a surveillance protocol were defined that satisfy the confidentiality needs of providers and ensure utility to public health. The authors developed a secure multi-party computation protocol using the Paillier cryptosystem to allow the disclosure of stratified case counts and denominators to meet these requirements. The authors evaluated the protocol in a simulated environment on its computation performance and ability to detect disease outbreak clusters.

RESULTS

Theoretical and empirical assessments demonstrate that all requirements are met by the protocol. A system implementing the protocol scales linearly in terms of computation time as the number of providers is increased. The absolute time to perform the computations was 12.5 s for data from 3000 practices. This is acceptable performance, given that the reporting would normally be done at 24 h intervals. The accuracy of detection disease outbreak cluster was unchanged compared with a non-secure distributed surveillance protocol, with an F-score higher than 0.92 for outbreaks involving 500 or more cases.

CONCLUSION

The protocol and associated software provide a practical method for providers to disclose patient data for sentinel, syndromic or other indicator-based surveillance while protecting patient privacy and the identity of individual providers.

A new and rapid genotypic assay for the detection of neuraminidase inhibitor resistant influenza A viruses of subtype H1N1, H3N2, and H5N1

The neuraminidase of influenza viruses is the target of the inhibitors oseltamivir and zanamivir. Recent reports on influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAI) are a cause for concern. Several amino acid substitutions, each as a consequence of one single nucleotide mutation, are known to confer resistance to NAI. An increase of NAI-resistant viruses appears to be likely as a result of a wider application of NAI for treatment and prophylaxis of seasonal influenza infections. Monitoring the occurrence and spread of resistant viruses is an important task. Therefore, RT-PCR assays were developed with subsequent pyrosequencing analysis (PSQ-PCR). These assays allow a rapid, high-throughput and cost-effective screening of subtype A/H1N1, A/H3N2, and A/H5N1 viruses. Various specimens such as respiratory swabs, allantoic fluid, or cell-propagated viruses can be used and results are available within hours. Several A/H1N1, A/H3N2, and A/H5N1 viruses isolated from human and avian specimens were tested to evaluate the method. Positive controls encoding resistance-associated mutations were created using site-directed mutagenesis. The results obtained with these controls showed that the assay can discriminate clearly the wild-type virus from a mutant virus. The detection limit of minor virus variants within the viral quasispecies amounts to 10%.

Virtual surveillance of communicable diseases: a 20-year experience in France

Inserm has developed, since 1984, an information system based on a computer network of physicians in France. It allows for constitution of large databases on diseases, with individual description of cases, and to explore some aspects of the mathematical theory of communicable diseases. We developed user-friendly interfaces for remote data entry and GIS tools providing real-time atlas of the epidemiologic situation in any location. The continuous and ongoing surveillance network is constituted of about 1200 sentinel voluntary and unpaid investigators. We studied their motivation, reasons for either withdrawal or compliance using survival analyses. We implemented early warning systems for outbreak detection and for time-space forecasting. We conducted epidemiological surveys for investigating outbreaks. Large available time and space series allowed us to calibrate and explore synchronism of influenza epidemics, to test the assumption of panmixing in susceptibles-infectious-removed type models and to study the role of closing school in influenza morbidity and mortality in elderly. More than 250 000 cases of influenza, 150 000 cases of acute diarrheas, 35,000 patients for whom HIV tests have been prescribed by general practitioners and 25,000 cases of chickenpox have been collected. Detection of regional influenza or acute diarrhea outbreaks and forecasting of epidemic trends three weeks ahead are currently broadcasted to the French media and published on Sentiweb on a weekly basis. Age-cohort-period models assessed field effectiveness of mass immunization strategies against measles and influenza in the country. Case-control studies with more than 1200 sets of cases of acute diarrheas and their matched controls showed the role of calicivirus and rotavirus as probable major causes of gastroenteritis during recurrent widespread outbreaks in winter in France. An age-specific model for chickenpox showed the probable role of children in disease transmission to their susceptible parents or grandparents. High level of synchronism between influenza epidemics has been demonstrated, either at a regional level (in France) or between France and the USA. The designation of our lab as a WHO collaborating center for electronic disease surveillance stimulates the development of global monitoring of diseases. We developed operational systems that are now available for the global monitoring of influenza (FluNet), and human and animal rabies (RABNET). Extension of electronic syndromic surveillance is needed in the world for improving surveillance capacities and real-time response against emerging diseases.

Geomedical warning system against epidemics

We describe aims, usage and evaluation of the computer-based early warning system telecommunication on medical events (TeCoMed), which achieves tracking down of temporal and spatial spread of epidemics for seasonal communicable diseases. It uses experiences from former waves of communicable diseases down to fine-grained local areas. Data is delivered by the biggest German insurance scheme. The results are presented by means of a commercial, geomedical information system. The evaluation of the system's performance concerning influenza shows that timely risk assessment and warnings are possible.

Building a sentinel surveillance system for sexually transmitted infections in Germany, 2003

BACKGROUND/OBJECTIVES

Increases in STIs have been reported from the United States and Europe. Since 2001, only syphilis and HIV are notifiable in Germany. A sentinel surveillance system has been set up to assess the occurrence and trends of STIs and identify risk groups.

METHODS

Through the sentinel system data are collected from local health offices (LHO), hospital based STI clinics and private practitioners (dermato-venerology, urology, gynaecology, or HIV). For every newly diagnosed laboratory confirmed infection of HIV, gonorrhoea, chlamydia, syphilis, or trichomoniasis physicians complete a standardised questionnaire regarding diagnosis, source of infection, and demographic information. Patients complete a questionnaire about sexual risk behaviour. The patient form is matched with the diagnosis form using a unique identifier number. Characteristics of sentinel patients were compared with those reported through the HIV and syphilis national notification system.

RESULTS

58 LHO, 14 hospital based STI clinics, and 160 private practitioners (53.1% dermato-venerologists) from all federal states participated in the study. 176 (75.9%) sentinel sites are located in cities of >100 000 inhabitants. From 1 March 2003-29 February 2004, a total of 1833 STIs have been reported, among them 452 chlamydia, 321 syphilis (10.9% of notified syphilis), 343 gonorrhoea, 269 HIV (15.7% of notified HIV). 925 (50.5%) of the patients were male, the median age was 31 years. Female patients were more often of foreign origin (chi(2) test; 70.0% v 26.3%; p<0.001).

CONCLUSIONS

Our sentinel system will provide a base for detection of STI trends in Germany. In addition, information about sexual risk behaviour will enable us to target prevention at those most at risk for STIs.

Sales of over-the-counter remedies as an early warning system for winter bed crises

OBJECTIVES

To evaluate the pattern of emergency adult medical admissions during the winter period and the usefulness of sales of over-the-counter cough/cold remedies as a predictor of these.

METHODS

The databases of a single NHS trust acute unit and pharmacy outlets in its catchment area were analyzed retrospectively, comparing numbers of emergency admissions, ICD-10 discharge codes, local electronic point-of-sale (EPOS) and national sales data.

RESULTS

Over nine consecutive winter periods from 1992/3, peak admissions always occurred within a defined ten-day period from 29th December to 9th January. Emergency admissions increased significantly during this period (P = 0.0002). Pharmaceutical/retail data were available for three consecutive winters 1998/99, 1999/2000 and 2000/2001, none of which coincided with increased influenza activity nationally. Acute respiratory illness as defined by International Classification of Diseases, 10th edition (ICD-10) discharge coding did not appear to contribute to the increase in admissions at the peak. However, National and Local EPOS sales were positively correlated with admissions and the rate of EPOS sales exceeded an empiric threshold of 1000 units per week two weeks prior to the admissions peak in each year.

CONCLUSIONS

Emergency admissions over the winter period are increasing and can be expected within a period of only ten days each year. No firm relationship between acute respiratory illness and admissions could be defined but local EPOS data may give up to two weeks warning of the peak in admissions and merits further prospective evaluation.

Application of a fluorogenic PCR assay for typing and subtyping of influenza viruses in respiratory samples

A fluorogenic PCR-based method (TaqMan-PCR) was developed for typing and subtyping of influenza virus genomes in clinical specimens. The TaqMan-PCR employs a probe technology that exploits the endogenous 5'-3' nuclease activity of the Taq DNA polymerase to allow direct detection of the amplicon by release of a fluorescent reporter during the PCR. Therefore, post-PCR analysis is avoided since hybridization with the fluorogenic probe and quantification of the amplified product is performed simultaneously during PCR cycling. The specificity of the method was evaluated on 86 influenza A (25 H1N1 and 61 H3N2) and 49 influenza B virus reference strains and isolates. The sensitivity of the technique was found to be at the level of 0.1 50% tissue culture infective dose. This TaqMan-PCR was applied prospectively to surveillance work by community-based sampling in Germany during the last two influenza seasons. Seven hundred five throat swabs were analyzed during the winter of 1997-1998. A total of 195 of 705 samples (28%) were positive by PCR. Influenza viruses could be isolated from 125 specimens (18%). During the 1998-1999 season, 1,840 respiratory samples were received. Influenza viruses were isolated from 281 specimens (15%) out of 525 throat swabs (29%) which were positive for influenza A or B virus by TaqMan-PCR. Further differentiation of influenza A virus-positive swabs revealed an intensive circulation of the subtype H3N2 during both seasons, 1997-1998 and 1998-1999. The TaqMan-PCR was much more sensitive than culture and revealed an excellent correlation for typing and subtyping of influenza viruses when samples were positive by both methods.

Survey on influenza laboratory diagnostic and surveillance methods in Europe. European Scientific Working Group on Influenza

The survey was undertaken by ESWI in order to investigate the comparability of the laboratory diagnostic methods and the influenza surveillance systems used in 24 European countries. The results indicate considerable consensus in the general approaches to collection and use of clinical specimens, rapid diagnostic techniques, virus isolation techniques in eggs or/and MDCK cell lines, virus identification and use of inhibition of hemagglutination (IHA) and complement fixation (CF) tests for serological diagnostics. However, the details of the techniques used are somewhat heterogeneous: antigen detection methods (immunofluorescence versus immuno adsorbent assay), isolation methods (eggs versus tissue culture), reagents (locally produced, WHO, commercial) are not always equivalent and results are therefore not really comparable. Some of these discrepancies are due to a lack of resources or a lack of priority for influenza in the country. The greatest differences between individual countries exist in the epidemiological part of surveillance programmes. The mode of collection of influenza related mortality and absentism from work varies considerably in different countries. These findings indicate the need to harmonize viral procedures and surveillance systems in European countries in order to improve validity and comparability of results and as a prerequisite for early information on influenza etiology and spread.

Forecasting disease risk for increased epidemic preparedness in public health

Emerging infectious diseases pose a growing threat to human populations. Many of the world's epidemic diseases (particularly those transmitted by intermediate hosts) are known to be highly sensitive to long-term changes in climate and short-term fluctuations in the weather. The application of environmental data to the study of disease offers the capability to demonstrate vector-environment relationships and potentially forecast the risk of disease outbreaks or epidemics. Accurate disease forecasting models would markedly improve epidemic prevention and control capabilities. This chapter examines the potential for epidemic forecasting and discusses the issues associated with the development of global networks for surveillance and prediction. Existing global systems for epidemic preparedness focus on disease surveillance using either expert knowledge or statistical modelling of disease activity and thresholds to identify times and areas of risk. Predictive health information systems would use monitored environmental variables, linked to a disease system, to be observed and provide prior information of outbreaks. The components and varieties of forecasting systems are discussed with selected examples, along with issues relating to further development.

Influenza and influenza-like illness in general practice: drawing lessons for surveillance from a pilot study in Paris, France

BACKGROUND

There are two types of inflenza surveillance techniques: qualitative laboratory-based surveillance and quantitative medical practice-based surveillance. The former is of great importance in isolating new strains of the virus, which helps in the decision-making process concerning the composition of the vaccine, and the latter provides estimates of morbidity, mortality or economic impact as a result of infection from the influenza virus. Rapid methods such as immunoflourescence (IF) or immunocapture assays (ICA) are now available for diagnosis of influenza infections. However, little is known about the use of these methods for influenza surveillance purposes.

AIMS

To evaluate the feasibility of a rapid influenza diagnosis in ambulatory conditions, and to investigate the therapeutical outcomes of patients suffering from influenza-like illness (ILI) in relation to the virological diagnoses.

METHOD

During the 1994-1995 influenza season, 130 patients presenting with ILI symptoms (< 36 hours) to 33 general practitioners (GPs) were included in a prospective study. Two nasal swabs and one throat swab per patient were collected and sent to the laboratory within 12 hours. Information concerning therapeutical outcomes was recorded during examination. Specimens were analysed using the immunofluorescence (IF) method and antigen immunocapture assay (ICA).

RESULTS

Sixteen influenza A (12%) and 19 influenza B (15%) infections were diagnosed. The overall rate of influenza positive specimens was 17% in the pre-epidemic period and 31% during the epidemic (P = 0.1). The rates of usable specimens for IF assay, nasal ICA and throat ICA were 46%, 100% and 99% respectively. The combination of these three collections ensured a highly sensitive influenza virological diagnosis. There were no differences in therapeutical outcomes between the influenza positive and negative cases. The GPs prescribed antibiotics in 60% of the cases for a mean duration of 7 days (+/- 1.2). The mean duration of sick leave was 3.4 days (+/- 1.6). Twelve patients (four influenza positive, eight influenza negative) had been vaccinated at the beginning of the winter. The practitioner's intuition concerning 'which patient should be tested for influenza virus' did not prove useful in improving the aptness of virological diagnoses in the field of influenza surveillance.

CONCLUSION

The only way to estimate the true impact of influenza is to carry out a systematic virological sampling based on a sensitive clinical definition and using sensitive laboratory methods.