influenza data in africa is scarce , and only 18 countries among the 46 in the whoafro region are able to perform laboratory diagnosis of influenza as previously reported . 
 , 
  in april 2009 , a sentinel network for influenza surveillance was set up in niamey , the capital city of niger . niger was one of the last countries affected by the recent a / h1n1 ( 2009 ) pandemic . in temperate countries , influenza transmission is influenced by temperature and humidity that explains its seasonality . 
  in tropical countries , contrary to humid tropical countries , niger is a sahelian country where dryness predominates over a very short rainy season . the effect of temperature at low values of humidity on influenza transmission is not clearly understood . better knowledge of the role of climatic factors could help when forecasting the occurrence of influenza epidemics , so as to limit their health impact . this work is therefore aimed at studying the link between some climatic factors , particularly temperature and humidity , and the occurrence of influenza in niamey . a sentinel surveillance network was set up in niamey in april 2009 and comprised of 10 sentinel sites . patients with influenza like illness ( ili ) or severe acute respiratory illness ( sari ) consulting at these sites were recruited between june 1 , 2009 and may 31 , 2010 . who clinical case definitions were used for ili and sari . a nasopharyngeal swab was sampled from each recruited patient and collected into a standard virus transport medium . detection and typing were performed according to the procedures of the national influenza centre , unit of molecular genetics of respiratory viruses , pasteur institute , paris . 

  in niger , the rainy season is from june to september , the hot season from october to november , the cold season from december to february and the very hot season from march to may . time series of daily counts of influenza cases and climatic factors were linked using a generalized additive model . minimal and maximal temperature , minimal and maximal relative humidity , wind speed and visibility routinely collected were analyzed ( visibility is defined as the maximal distance from which a fixed object or light can be clearly seen ) . trend , seasonality , day of the week , holidays , religious festivals , and pilgrimage were taken into account in the model . the package mgcv ( multifold generalized crossvalidation ) was used to control seasonal and longterm temporal trends and to minimize autocorrelation in the residuals . , 
  the quality of the model adjustment was checked using partial autocorrelation function , residuals and predicted data versus observed data . the choice of the final model was based on the akaike information criteria ( aic ) . a total of 320 patients consulting at the sentinel sites were recruited . among them , 76 ( 23.8% ) were confirmed positive for influenza and consisted of 46 a / h1n1(2009 ) , 19 a / h3n2 and 11 influenza b , with the median age of 7 ( interquartile range  =  216  years ) , 6 ( interquartile range  =  214.5  years ) and 7  years ( interquartile range  =  4.58  years ) , respectively . the 244 negative patients had a median of age of 5.5  years ( interquartile range  =  1.827.3  years ) . thirtynine per cent ( 39% ) of the patients recruited during the cold season were confirmed positive for influenza as well as for 34.4% , 20.2% , and 15.8% during the rainy , the very hot , and the hot seasons respectively ( figure  1 ) . all the a / h1n1 ( 2009 ) cases were detected between february 2 and april 8 , 2010 . distribution of the different influenza viruses by season in niamey , niger ( 20092010 ) . proportion of positive cases for influenza and description of climatic factors according to the seasons q1 , first quartile ; q3 , third quartile . hot season : 1st october to 14 december 2009 . * * cold season : 15 december 2009 to 13 february 2010 . * * * very hot season : 14 february to 31 may 2010 . influenza cases increased significantly with minimal temperatures between 13 and 22c (   =  3.99 , se  =  1.74 , p  =  0.022 ) . increase in influenza cases occurred with visibility 9500  m , values encountered during the rainy season (   =  3.30 , se  =  1.34 , p  =  0.014 ) . the preliminary results indicated that temperature and visibility were significantly correlated with the occurrence of influenza in niamey . the majority of influenza cases were detected at low minimal temperatures during the cold season and the rainy season . . 

  with guinea pig model infected by a / h3n2 virus ( influenza a / panama/2007/99 virus ) supports this result . indeed , high values for maximal temperatures ( > 30c ) are observed almost all year around in niamey . davidwest and cook observed that in nigeria , major outbreaks of ili and sari occurred at the lowest temperatures when the dry and dusty harmattan winds blow from november to march . 
  in this study , the transmission was efficient even at very low values of relative humidity observed during the cold season . however , a study by hanley and borup showed that below 20% of relative humidity and irrespective of temperature , influenza transmission remains poorly known . influenza was predominant during the rainy season when visibility was observed at its highest values and in climatic conditions closer to those which are observed in humid tropical countries . visibility was found to be correlated with occurrence of influenza cases but was in fact probably more of a surrogate factor . indeed during rainy days , close contact favors virus transmission likely because people stay home for longer periods of time . in this work , relative humidity was not retrieved as a significant climatic factor contrary to studies on the incidence of influenza a virus in argentina and hong kong . , 
  the role of humidity on influenza transmission efficiency is not well established in the tropics . indeed , influenza generally leads to symptoms similar to malaria , and patients frequently treat themselves or consult the healthcare facilities only in case of serious disease . second , the results of this analysis concerned only the main healthcare facilities within niamey , the capital city of niger . the patients recruited in the study , however , came from different quarters of niamey and concerned all socioeconomic classes ( data not shown ) . these results are in favor of a predominant seasonality of influenza during the cold and rainy seasons . during these seasons , positive patients were more frequently detected even though the influenza virus could circulate all year round in niamey . this work provides a new insight into higher influenza transmission during low temperatures , even at the lowest values of relative humidity . further work is ongoing in niger to provide more information regarding the link between climatic factors and influenza , as well as its seasonality .