Abstract
Background
Temporal clusters of salmonellosis are believed to occur but have not been quantitatively explored, thus, our objectives were to describe trends, seasonal patterns, and clusters of salmonellosis in humans in Alberta by examining isolates reported through passive surveillance systems.
Methods
Cases of salmonellosis reported through Notifiable Disease Records between January 1990 and December 2001 were obtained from Alberta Health and Wellness. Least squares regression was used to characterize the distribution (long-term trends and seasonal patterns) of isolates. A cluster detection test was used to determine if and when isolates of specific serovars aggregated in time, over and above the background distribution. Comparisons were made to temporal patterns in Alberta livestock and to known outbreaks in humans.
Results
S. Typhimurium, Enteritidis, Hadar, Heidelberg, and Thompson were the five most common serovars of the 9,188 isolates reported. The annual number of isolates was relatively stable over time, with a distinct summertime seasonal pattern. Clusters were observed in 23 of 32 serovars examined. More clusters occurred in September and October than in other months, and in 1998 through 2001 than in the early to mid-1990s. Also, more clusters were of short duration than long.
Interpretation
Short-duration clusters likely indicate a point source of infection, while long-duration clusters may indicate exposure to a persistent common source or the occurrence of secondary infections. A sharp increasing trend and a large cluster of S. Heidelberg may have public health implications. Surveillance activities focussed on similarities between common serovars, trends, and temporal clusters in humans and animals, and studies on factors associated with autumn clusters may be useful in preventing outbreaks in humans.
Résumé
Contexte
On estime qu’il se forme des grappes temporelles de cas de salmonellose qui n’ont pas encore fait l’objet d’études quantitatives. Aussi, notre étude visait à dégager les tendances, les schémas saisonniers et les grappes de la salmonellose chez les habitants de l’Alberta en examinant les isolats détectés par des systèmes de surveillance passive.
Méthodes
Après en avoir fait la demande, on a obtenu auprès du ministère de la santé et du mieux-être (Ministry of Health and Wellness) de l’Alberta les cas de salmonellose signalés et inscrits dans les documents relatifs aux maladies à déclaration obligatoire pour la période allant de janvier 1990 à décembre 2001. On a utilisé la technique de régression des carrés pour caractériser la distribution des isolats (de même que les tendances à long terme et les schémas saisonniers). Un test de détection des grappes a permis de déterminer la présence éventuelle d’isolats des sérovars particuliers agrégés et le moment de leur agrégation, indépendamment de la distribution naturelle. L’analyse comparative a visé les schémas temporels du bétail albertain et les flambées connues chez les humains.
Résultats
S. Typhimurium, Enteritidis, Hadar, Heidelberg et Thompson représentaient les cinq sérovars les plus courants parmi les 9 188 signalés. Le nombre d’isolats signalés était relativement stable au cours des années même si on constatait une tendance distincte au cours de la saison estivale. On a observé la présence de grappes chez 23 des 32 sérovars examinés. On a relevé plus de grappes au cours des mois de septembre et d’octobre qu’au cours des autres mois et entre 1998 et 2001 que durant la période s’échelonnant du début au milieu des années 1990. En outre, davantage de grappes étaient de courte durée.
Interprétation
Les grappes de courte durée indiquent vraisemblablement une source ponctuelle d’infection tandis que celles de longue durée pourraient indiquer une exposition à une source constante et commune ou à la présence d’infections secondaires. Une nette tendance à la hausse et une grappe importante de cas de S. Heidelberg sont susceptibles d’avoir des répercussions sur la santé publique. Les activités de surveillance ont surtout visé les similitudes entre les sérovars, les tendances et les grappes temporelles communes chez les humains et les animaux. La réalisation d’études sur les facteurs rattachés aux grappes durant l’automne pourrait contribuer à prévenir les flambées chez les humains.
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Guerin, M.T., Martin, S.W. & Darlington, G.A. Temporal Clusters of Salmonella Serovars in Humans in Alberta, 1990–2001. Can J Public Health 96, 390–395 (2005). https://doi.org/10.1007/BF03404039
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DOI: https://doi.org/10.1007/BF03404039