title: Associations between environmental factors and hospital admissions for sickle cell disease.
abstract: Sickle cell disease is an increasing global health burden. This inherited disease is characterized by a remarkable phenotypic heterogeneity, which can only partly be explained by genetic factors. Environmental factors are likely to play an important role but studies of their impact on disease severity are limited and their results are often inconsistent. This study investigated associations between a range of environmental factors and hospital admissions of young patients with sickle cell disease in London and in Paris between 2008 and 2012. Specific analyses were conducted for subgroups of patients with different genotypes and for the main reasons for admissions. Generalized additive models and distributed lag non-linear models were used to assess the magnitude of the associations and to calculate relative risks. Some environmental factors significantly influence the numbers of hospital admissions of children with sickle cell disease, although the associations identified are complicated. Our study suggests that meteorological factors are more likely to be associated with hospital admissions for sickle cell disease than air pollutants. It confirms previous reports of risks associated with wind speed (risk ratio: 1.06/standard deviation; 95% confidence interval: 1.00-1.12) and also with rainfall (1.06/standard deviation; 95% confidence interval: 1.01-1.12). Maximum atmospheric pressure was found to be a protective factor (0.93/standard deviation; 95% confidence interval: 0.88-0.99). Weak or no associations were found with temperature. Divergent associations were identified for different genotypes or reasons for admissions, which could partly explain the lack of consistency in earlier studies. Advice to patients with sickle cell disease usually includes avoiding a range of environmental conditions that are believed to trigger acute complications, including extreme temperatures and high altitudes. Scientific evidence to support such advice is limited and sometimes confusing. This study shows that environmental factors do explain some of the variations in rates of admission to hospital with acute symptoms in sickle cell disease, but the associations are complex, and likely to be specific to different environments and the individual's exposure to them. Furthermore, this study highlights the need for prospective studies with large numbers of patients and standardized protocols across Europe.
authors.affiliation: Department of Epidemiology and Biostatistics, MRC-PHE Centre for Environment and Health, School of Public Health, Imperial College London, UK f.piel@imperial.ac.uk.|Department of Zoology, University of Oxford, UK.
authors.forename: Frédéric B
authors.initials: FB
authors.lastname: Piel
authors.affiliation: Department of Molecular Haematology, King's College London School of Medicine, King's College Hospital, UK.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Tewari
authors.affiliation: Reference Centre for Sickle-Cell Disease, Pediatric Department, Hôpital Universitaire Necker-Enfants Malades, APHP, Paris, Université Paris Descartes, France.
authors.forename: Valentine
authors.initials: V
authors.lastname: Brousse
authors.affiliation: Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, Greece.
authors.forename: Antonis
authors.initials: A
authors.lastname: Analitis
authors.affiliation: Environmental Research Group, MRC-PHE Centre for Environment and Health, King's College London, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Font
authors.affiliation: Department of Molecular Haematology, King's College London School of Medicine, King's College Hospital, UK.
authors.forename: Stephan
authors.initials: S
authors.lastname: Menzel
authors.affiliation: Department of Molecular Haematology, King's College London School of Medicine, King's College Hospital, UK.
authors.forename: Subarna
authors.initials: S
authors.lastname: Chakravorty
authors.affiliation: Department of Molecular Haematology, King's College London School of Medicine, King's College Hospital, UK.|National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Swee Lay
authors.initials: SL
authors.lastname: Thein
authors.affiliation: Department of Paediatric Haematology, Evelina Children's Hospital, King's College London, UK.
authors.forename: Baba
authors.initials: B
authors.lastname: Inusa
authors.affiliation: Department of Paediatric Haematology and Oncology, Barts Health NHS Trust, Royal London Hospital, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Telfer
authors.affiliation: Reference Centre for Sickle-Cell Disease, Pediatric Department, Hôpital Universitaire Necker-Enfants Malades, APHP, Paris, Université Paris Descartes, France.
authors.forename: Mariane
authors.initials: M
authors.lastname: de Montalembert
authors.affiliation: Environmental Research Group, MRC-PHE Centre for Environment and Health, King's College London, UK.
authors.forename: Gary W
authors.initials: GW
authors.lastname: Fuller
authors.affiliation: Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, Greece.|Environmental Research Group, MRC-PHE Centre for Environment and Health, King's College London, UK.
authors.forename: Klea
authors.initials: K
authors.lastname: Katsouyanni
authors.affiliation: Department of Molecular Haematology, King's College London School of Medicine, King's College Hospital, UK.
authors.forename: David C
authors.initials: DC
authors.lastname: Rees
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000755:Anemia, Sickle Cell / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D004777:Environment; D004781:Environmental Exposure / Q000009:adverse effects; D006760:Hospitalization; D006801:Humans; D008131:London / Q000453:epidemiology; D008875:Middle Aged; D016017:Odds Ratio; D010297:Paris / Q000453:epidemiology; D062486:Public Health Surveillance; D012307:Risk Factors; D055815:Young Adult