ABSTRACT
The burden of influenza was estimated from surveillance data in Tunisia using epidemiological parameters of transmission with WHO classical tools and mathematical modelling. The incidence rates of influenza-associated influenza-like illness (ILI) per 100 000 were 18 735 in 2012/2013 season; 5536 in 2013/14 and 12 602 in 2014/15. The estimated proportions of influenza-associated ILI in the total outpatient load were 3.16%; 0.86% and 1.98% in the 3 seasons respectively. Distribution of influenza viruses among positive patients was: A(H3N2) 15.5%; A(H1N1)pdm2009 39.2%; and B virus 45.3% in 2014/2015 season. From the estimated numbers of symptomatic cases, we estimated that the critical proportions of the population that should be vaccinated were 15%, 4% and 10% respectively. Running the model for the different values of R0, we quantified the number of symptomatic clinical cases, the clinical attack rates, the symptomatic clinical attack rates and the number of deaths. More realistic versions of this model and improved estimates of parameters from surveillance data will strengthen the estimation of the burden of influenza.
Subject(s)
Cost of Illness , Influenza A Virus, H1N1 Subtype/isolation & purification , Influenza A Virus, H3N2 Subtype/isolation & purification , Influenza, Human/epidemiology , Models, Theoretical , Seasons , Adolescent , Adult , Aged , Child , Child, Preschool , Female , Humans , Incidence , Infant , Male , Middle Aged , Models, Statistical , Population Surveillance , Tunisia , Young AdultABSTRACT
The burden of influenza was estimated from surveillance data in Tunisia using epidemiological parameters of transmission with WHO classical tools and mathematical modelling. The incidence rates of influenza-associated influenza-like illness [ILI] per 100 000 were 18 735 in 2012/2013 season; 5536 in 2013/14 and 12 602 in 2014/15. The estimated proportions of influenza-associated ILI in the total outpatient load were 3.16%; 0.86% and 1.98% in the 3 seasons respectively. Distribution of influenza viruses among positive patients was: A[H3N2] 15.5%; A[H1N1] pdm2009 39.2%; and B virus 45.3% in 2014/2015 season. From the estimated numbers of symptomatic cases, we estimated that the critical proportions of the population that should be vaccinated were 15%, 4% and 10% respectively. Running the model for the different values of R0, we quantified the number of symptomatic clinical cases, the clinical attack rates, the symptomatic clinical attack rates and the number of deaths. More realistic versions of this model and improved estimates of parameters from surveillance data will strengthen the estimation of the burden of influenza
En Tunisie, la charge de la grippe a été estimée à partir des données de surveillance, en utilisant les paramètres épidémiologiques de la transmission avec les outils classiques de l'OMS et la modélisation mathématique. Les taux d'incidence des syndromes de type grippal [STG] associés à la grippe étaient 18 735 pour 100 000 pour la saison 2012-2013 ; 5 536 pour 2013-2014 et 12 602 pour 2014-2015. La part estimée de STG associés à la grippe pour la charge totale de patients externes était respectivement de 3,16%, 0,86% et 1,98% pour les trois saisons. Parmi les patients positifs au virus de la grippe, la répartition était la suivante pour la saison 2014-2015 : 15,5% pour le virus A[H3N2] ; 39,2% pour le virus A[H1N1]pdm2009 ; et 45,3% pour le virus B. A partir du nombre estimé de cas symptomatiques, nous avons calculé que la proportion critique de la population devant être vaccinée était respectivement de 15%, 4% et 10%. L'exécution du modèle avec les différentes valeurs de R0 nous a permis de déterminer le nombre de cas cliniques symptomatiques, les taux d'attaque clinique, les taux d'attaque clinique pour les cas symptomatiques et le nombre de décès. Des versions plus réalistes de ce modèle ainsi que des estimations améliorées des paramètres issus des données de surveillance permettront d'accroître l'utilité des modèles mathématiques
Subject(s)
Communicable Diseases , Influenza, Human , Seasons , Influenza A Virus, H1N1 SubtypeABSTRACT
OBJECTIVE: The authors had for aim to characterize influenza B strains having circulated in Tunisia to identify new mutations and compare them with reference strains. METHODS: The epidemiological surveillance of influenza allowed identifying 19 patients with symptoms related to respiratory infection, who had been infected by influenza B strains isolated in several regions of Tunisia in 2009-2010 and in 2010-2011. Laboratory identification and detection of mutations in the segment encoding hemagglutinin of influenza viruses was performed by real time PCR and sequencing. RESULTS: The two influenza B Tunisian strains of the 2009-2010 season belonged to the Victoria lineage, whereas 2010-2011 season strains belonged to B/Victoria/2/87 and B/Yamagata/16/88 lineages with a dominance of the Yamagata lineage (76%). This study allowed identifying amino acid substitutions: T121A, S150I, N165Y, T181A, G183R, D196N, S229D, M251V and K253R in the B/Yamagata lineage; L58P, N75K, K109N, N165K, S172P and K257R into the B/Victoria lineage. These mutations were specific of Tunisian groups of variants. Most influenza B-Yamagata lineage viruses (69%) were associated with severe cases. CONCLUSION: Molecular analysis of the various influenza B strains circulating in Tunisia is useful to detect new mutations that can modify the phenotype of influenza strains.
