Spatio-temporal factors associated with meningococcal meningitis annual incidence at the health centre level in Niger, 2004-2010.
BACKGROUND
Epidemics of meningococcal meningitis (MM) recurrently strike the African Meningitis Belt. This study aimed at investigating factors, still poorly understood, that influence annual incidence of MM serogroup A, the main etiologic agent over 2004-2010, at a fine spatial scale in Niger.


RESULTS
To take into account data dependencies over space and time and control for unobserved confounding factors, we developed an explanatory Bayesian hierarchical model over 2004-2010 at the health centre catchment area (HCCA) level. The multivariate model revealed that both climatic and non-climatic factors were important for explaining spatio-temporal variations in incidence: mean relative humidity during November-June over the study region (posterior mean Incidence Rate Ratio (IRR) = 0.656, 95% Credible Interval (CI) 0.405-0.949) and occurrence of early rains in March in a HCCA (IRR = 0.353, 95% CI 0.239-0.502) were protective factors; a higher risk was associated with the percentage of neighbouring HCCAs having at least one MM A case during the same year (IRR = 2.365, 95% CI 2.078-2.695), the presence of a road crossing the HCCA (IRR = 1.743, 95% CI 1.173-2.474) and the occurrence of cases before 31 December in a HCCA (IRR = 6.801, 95% CI 4.004-10.910). At the study region level, higher annual incidence correlated with greater geographic spread and, to a lesser extent, with higher intensity of localized outbreaks.


CONCLUSIONS
Based on these findings, we hypothesize that spatio-temporal variability of MM A incidence between years and HCCAs result from variations in the intensity or duration of the dry season climatic effects on disease risk, and is further impacted by factors of spatial contacts, representing facilitated pathogen transmission. Additional unexplained factors may contribute to the observed incidence patterns and should be further investigated.
Unité d'Epidémiologie des Maladies Emergentes, Institut Pasteur, Paris, France; Univ. Pierre et Marie Curie, Cellule Pasteur UPMC, Paris, France.
Juliette
J
Paireau
Unité d'Epidémiologie/Santé-Environnement-Climat, Centre de Recherche Médicale et Sanitaire (CERMES)/Réseau International des Instituts Pasteur, Niamey, Niger.
Halima B
HB
Maïnassara
Unité d'Epidémiologie/Santé-Environnement-Climat, Centre de Recherche Médicale et Sanitaire (CERMES)/Réseau International des Instituts Pasteur, Niamey, Niger.
Jean-François
JF
Jusot
Unité de Biologie, Centre de Recherche Médicale et Sanitaire (CERMES)/Réseau International des Instituts Pasteur, Niamey, Niger.
Jean-Marc
JM
Collard
Unité d'Epidémiologie/Santé-Environnement-Climat, Centre de Recherche Médicale et Sanitaire (CERMES)/Réseau International des Instituts Pasteur, Niamey, Niger.
Issa
I
Idi
Unité d'Epidémiologie/Santé-Environnement-Climat, Centre de Recherche Médicale et Sanitaire (CERMES)/Réseau International des Instituts Pasteur, Niamey, Niger.
Jean-Paul
JP
Moulia-Pelat
Unité d'Epidémiologie des Maladies Emergentes, Institut Pasteur, Paris, France; EHESP French School of Public Health, Sorbonne Paris Cité, Rennes, France.
Judith E
JE
Mueller
Unité d'Epidémiologie des Maladies Emergentes, Institut Pasteur, Paris, France; Conservatoire National des Arts et Métiers, Chaire Santé et Développement, Paris, France.
Arnaud
A
Fontanet
D001499:Bayes Theorem; D006801:Humans; D015994:Incidence; D008585:Meningitis, Meningococcal / Q000453:epidemiology*; D009548:Niger / Q000453:epidemiology; D011634:Public Health; D012189:Retrospective Studies; D062211:Spatio-Temporal Analysis