Original ArticleInfluenza-like illness criteria were poorly related to laboratory-confirmed influenza in a sentinel surveillance study
Introduction
Influenza illness is a highly contagious infectious disease, annual epidemics occurring typically in the Northern Hemisphere between December and April [1]. Major changes on influenza A viruses have led to periodic emergence of pandemics, during which the rates of morbidity and mortality increase [2].
Influenza disease is subjected to surveillance worldwide by national networks that predict the epidemic threshold by reporting clinical and virological data [3]. World Health Organization encourages reinforcing influenza surveillance systems, because they provide data about the occurrence of a new influenza A virus subtype [2]. In an influenza surveillance network, patients from whom throat and/or nasal samples are collected must fulfill a clinical case definition [3]. Sample collection in most surveillance systems is made by using the clinical criteria of influenza-like illness (ILI) or acute respiratory infection (ARI) [3], the later being a less restrictive definition than the ILI criteria. In Spain, sentinel physicians follow the clinical criteria of ILI [3]. ILI has been defined by the Classification Committee of the World Organization of Family Doctors [4] (ICHPPC-2) by the presence of six of nine symptoms, though other authors have adopted the criteria of ILI as defined by the presence of fever plus two of the following four symptoms: headache, cough, sore throat, and myalgia [5], [6].
The present study analyzes the most related clinical data for influenza and the utility of ILI as defined by the ICHPPC-2 criteria in the context of the sentinel surveillance network in Andalusia (Spain) during a 3-year period.
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Methods
As part of the sentinel surveillance network for influenza disease in Spain, throat samples and clinical data from outpatients were collected by 20 sentinel physicians (17 general practitioners and 3 pediatricians) during three periods of influenza surveillance, October 2000 to May 2001 (Period 1), October 2001 to May 2002 (Period 2), and October 2002 to May 2003 (Period 3). Inclusion criteria comprised persons of all ages with clinical evidence of ARI over a duration of ≤72 hours. ARI was
Results
A total of 1,934 patients with ages ranging between 2 months and 96 years (mean age ± standard deviation = 25.09 ± 22.99) were studied: 541 in period 1, 668 in period 2, and 725 in period 3. Patient characteristics by age groups are shown in Table 1: sex, vaccination status, and influenza virus isolations. From the 1934 throat specimens processed, 359 yielded positive results for influenza viruses (18.56%), 173 influenza A viruses (48.2% of total isolations), and 186 influenza B (51.8% of total
Discussion
The distribution of the population in the present study shows that almost 50% correspond to a pediatric population. Although the percentage is high, it is not surprising, because children are the main reservoir of respiratory viruses and attack rates are higher in this population [9], [10]. We note that the pediatric population was also attended by some general practitioners from the sentinel network (apart from the three pediatricians), which may have contributed in part to the increased
Acknowledgments
Authors are indebted to María del Mar Rodríguez del Águila, Servicio de Bioestadística del Hospital Universitario Virgen de las Nieves, Granada, for helping in the statistical analysis of the data.
References (23)
The impact of influenza in children
Semin Pediatr Infect Dis
(2002)- et al.
A prospective, community-based study on virologic assessment among elderly people with and without symptoms of acute respiratory infection
J Clin Epidemiol
(2003) - et al.
The impact of influenza viruses on hospitalizations in infants younger than two years old during epidemics of respiratory syncytial virus infection
Clin Microbiol Infect
(2003) Clinical features of influenza
Semin Respir Infect
(1992)- World Health Organization. Influenza pandemic preparedness plan: the role of WHO and guidelines for national or...
- European Influenza Surveillance Scheme (EISS). Annual report: 2000–2001 influenza season. Utrecht, December 2001...
Inclusion criteria for the use of the rubrics of the International Classification of Health Problems in Primary Care
- et al.
Diagnosis of influenza in the community: relationship of clinical diagnosis to confirmed virological, serologic, or molecular detection of influenza
Arch Intern Med
(2001) - et al.
Predicting influenza infections during epidemics with use of a clinical case definition
Clin Infect Dis
(2000) - et al.
Rapid detection of respiratory viruses by shell vial assay using simultaneous culture of HEp-2, LLC-MK2, and MDCK cells in a single vial
J Clin Microbiol
(1999)
Hemagglutination and hemagglutination-inhibition test
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Influenza Surveillance Network in Andalusia, Spain: Carmen Petit-Gancedo, Mercedes Sánchez-Lanuza, Ángeles Oteros-Corpas, Francisco Sánchez-Prados, José Gil-Martín, Nuria Martínez-Moral, Fernando de Osma-Rodríguez, Juan Antonio Navarro-González, Mercedes Barón-Crespo, Francisca Ceínos-Vicente, Rafael Bejarano-Cielos, Dolores Rueda-Lozano, Javier Sánchez Ruiz-Cabello, José Luis Schiaffino-Cano, Dolores Corrochano-Dalí, Giordano López-Tierra, Gregorio Martos-Toribio, Manuel Zafra-Garrido, Carlos Guerra-García, José Manuel Andrade-López, Manuel Cid-Chavero, Manuel Caraballo-Ávila.