RSV Seasonality in Martinique in Children Aged 2 Years or Less
Condition: Bronchiolitis; Respiratory Syncytial Virus
MeSH terms: Bronchiolitis
Study type: Observational

Summary: 
      The epidemiological characteristics of RSV bronchiolitis differ between tropical and
      temperate zones. This study seeks to understand which climatic factors could influence the
      specific seasonality of these bronchiolitis in Martinique and to verify the hypothesis put
      forward: influence of favorable climatic conditions in the month preceding the start of the
      epidemic. In addition, the study will improve our knowledge of the epidemiology of the
      infection in order to improve the management of infants.
    

Detailed description: 
      Respiratory Syncytial Virus (RSV) infections are the leading cause of hospitalization for
      respiratory distress in infants (50% of children under 1 year of age are infected with the
      virus, 100% of children under 3 years of age). They are responsible for 66,000 to 199,000
      deaths in children under 5 years of age worldwide, and 15,000 to 20,000 hospitalizations in
      France depending on the year. It is a highly contagious virus whose transmission is both
      respiratory and by hand and which appreciates humidity to develop.

      In temperate regions where this infection has been well studied, it occurs preferentially
      during the winter, probably favoured by the cold and humidity, as well as by the confinement
      of individuals during this season. The more the child is young, premature, has a chronic
      respiratory pathology or congenital heart disease, the more sever the disease. Prevention is
      based on the injection of a monoclonal antibody (Palivizumab) before the start of the
      epidemic season and on conventional hygiene measures. But today, little epidemiological data
      is available for tropical regions and in Martinique, which makes it impossible to understand
      why, how and when RSV develops on our island. Some epidemiological studies carried out in
      tropical regions point to the possibility that the humidity in the air would favour viral
      development and in fact, these epidemics are more frequently found during the rainy season.
      The humidity level, the number of rainy days, the rate of sunshine and cloud cover, and
      finally the importance of the wind, could explain a different seasonality from that known in
      temperate regions (seasonality being linked to the virus circulation patterns and being
      defined as the ability to re-emerge at the same period from one year to the next).

      Research issues A first study carried out at the University hospital of Martinique over a
      period of 2 years (from July 1, 2007 to December 31, 2008) has made it possible to specify
      the epidemiology a little better but the results need to be confirmed. This work seems to
      show that the epidemic starts earlier than in temperate zones: (late August - early September
      to late November - early December) versus (November - December to March - April)
      respectively. The number of cases per epidemic can change significantly (factor 2.5).
      However, this first study was not long enough to ensure that the seasonality identified will
      be systematically repeated from one year to the next. Moreover, this study did not allow us
      to specify the number of children with clinical severity criteria on our island.

      By carrying out a study over a longer period, the investigators will have a better
      understanding of seasonality and the rate of disease in children in Martinique, allowing us
      to better anticipate the extent and severity of these phenomena. This precision will allow us
      to determine when to start Monoclonal Antibody injections for vulnerable children
      (essentially infants with chronic respiratory pathologies or congenital cardiac pathologies,
      i.e. approximately 30 children per year in Martinique). The investigators will also be able
      to anticipate future needs of beds and caregivers to the epidemic to come or in progress. The
      investigators will therefore have better preventive care for children at risk and better
      preparation of the healthcare offer.

      Research questions

        -  Descriptions of the characteristics of RSV bronchiolitis epidemics (seasonality, rate of
           occurrence, case profile)?

        -  What are the factors that may explain a specific seasonality and case rate in tropical
           zones, especially Martinique? What is the role of climatic factors?

      Research hypotheses The investigators believe that the seasonality and characteristics of RSV
      bronchiolitis are indeed specific to tropical areas such as Martinique.

      The investigators hypothesize that, in tropical areas, certain favourable climatic
      conditions, prevailing in the month prior to the usual period of RSV bronchiolitis outbreak
      onset or during the epidemic, would be intrinsically linked to the characteristics of these
      epidemics.

      Indeed, RSV is a virus that particularly likes humid atmospheres in which to develop. These
      conditions are conducive during the rainy season in the tropics (second half of the year in
      Martinique), which could explain a different seasonality from that known in temperate regions
      (where the epidemic occurs rather during the winter). These favourable climatic conditions
      can be approximated by measuring the humidity level, the number of rainy days, the average
      temperature, the rate of sunshine and cloud cover and the average wind strength. In addition,
      respiratory irritants such as sand mist or other air pollution, as assessed by the air
      quality index, could be among the parameters that explain these differences.

      The investigators propose to retrospectively analyze 12 years of hospital data on RSV
      bronchiolitis cases in Martinique among hospitalized children 2 years of age and younger, the
      main targets of RSV, and therefore the population most vulnerable to this virus. The
      investigators will focus only on hospitalized patients because they are the most severely
      affected patients, which will allow us to accurately describe the clinical severity criteria
      in this at-risk population.

      Main objective Describe the temporal distribution of RSV bronchiolitis cases in children 2
      years of age or younger hospitalized in Martinique, over a 12-year period (2007 to 2018),
      based on climatic parameters prevailing in the month before the beginning of the epidemic or
      during the epidemic.

      Secondary objectives

        -  Describe the weekly and monthly distribution of RSV bronchiolitis, over the 12-year
           study period, among children 2 years of age and younger hospitalized in Martinique.

        -  Describe the characteristics of each epidemic observed over the study period.

        -  Describe the characteristics of RSV bronchiolitis cases during the study period.

        -  Analyze the association between the climatic parameters studied and the occurrence of
           RSV bronchiolitis.
    

Observational model: Case-Only
Time perspective: Retrospective
Sampling method: Probability Sample
Study population: 
        children 2 years of age or younger hospitalized in Martinique with RSV bronchiolitis cases,
        over a 12-year period (2007 to 2018)
      
Keywords: Bronchiolitis; Respiratory Syncytial Virus; Child; Infant, premature; Bronchopulmonary Dysplasia; Heart Defects, Congenital; Tropical climate; Humidity; Epidemiology; Air pollution