Nasal Colonization of Humans with Methicillin-Resistant Staphylococcus aureus (MRSA) CC398 with and without Exposure to Pigs

Abstract

BackgroundStudies in several European countries and in North America revealed a frequent nasal colonization of livestock with MRSA CC398 and also in humans with direct professional exposure to colonized animals. The study presented here addresses the question of further transmission to non exposed humans.MethodsAfter selecting 47 farms with colonized pigs in different regions of Germany we sampled the nares of 113 humans working daily with pigs and of their 116 non exposed family members. The same was performed in 18 veterinarians attending pig farms and in 44 of their non exposed family members. For investigating transmission beyond families we samples the nares of 462 pupils attending a secondary school in a high density pig farming area. MRSA were detected by direct culture on selective agar. The isolates were typed by means of spa-sequence typing and classification of SCCmec elements. For attribution of spa sequence types to clonal lineages as defined by multi locus sequence typing we used the BURP algorithm. Antibiotic susceptibility testing was performed by microbroth dilution assay.ResultsAt the farms investigated 86% of humans exposed and only 4.3% of their family members were found to carry MRSA exhibiting spa-types corresponding to clonal complex CC398. Nasal colonization was also found in 45% of veterinarians caring for pig farms and in 9% of their non exposed family members. Multivariate analysis revealed that antibiotic usage prior to sampling beard no risk with respect to colonization. From 462 pupils only 3 were found colonized, all 3 were living on pig farms.ConclusionThese results indicate that so far the dissemination of MRSA CC398 to non exposed humans is infrequent and probably does not reach beyond familial communities.

Outbreak of Methicillin-Resistant Staphylococcus aureus ST398 in a Dutch Nursing Home

“…5,6 However, this outbreak of MRSA ST398 in a community setting shows that substantial humanto-human transmission can occur. Further adaptation to humans may occur, and if MRSA ST398 can successfully spread from human to human, it may pose a significant public health problem in the future.…”

“…Transmission within families, as well as single cases of colonized healthcare workers, have been described. 2,5 However, up to now there have been few reports of transmission of MRSA ST398 in healthcare settings. In the hospital setting, MRSA ST398 is reported to be less transmissible than other MRSA types.…”

L’histoire de Staphylococcus aureus ST398 : un paradigme médical du 21ème siècle

“…La co-résistance aux antibiotiques des souches SARM d'origine porcine ou humaine est variable, elle est surtout rapportée vis-à-vis des seuls antibiotiques de la famille des tétracyclines, plus rarement de ceux de la famille des macrolides (van Loo et al 2007;Cuny et al 2009;Denis et al 2009;E. Jouy, comm.…”

“…Dans l'enquête conduite dans plusieurs régions d'Allemagne entre septembre 2007 et janvier 2009, 921 souches de SARM ont été isolées respectivement chez des porcs et leurs éleveurs (47 fermes), 100 % des souches étaient résistantes à l'oxyté-tracycline (OT). Le pourcentage de souches OT-R était de 18 % contre 30 % pour les souches OT.Erythromycine.Clindamycine-R. D'autres phénotypes de résistance (< 11% des souches) sont rapportés tant vis-à-vis du co-trimoxazole que d'un aminoside comme la gentamicine, la résistance vis-à-vis des fluoroquinolones comme la ciprofloxacine ou la moxifloxacine restant faible (< 4%) (Cuny et al 2009). Quelques données concernent l'identification de plusieurs gènes de résistance tels tetK, tetM, ermA, ermC ou encore ant4'et aph2-aac6' (Witte et al 2007 ;Denis et al 2009).…”

“…Le portage nasal chez l'homme a été rapporté avec des fréquences très variables, surtout chez des professionnels, c'est-à-dire les éle-veurs de porc, les vétérinaires, voire les employés d'abattoir (Armand-Lefevre et al 2005 ;van Loo et al 2007 ;Lewis et al 2008 ;van Belkum et al 2008 ;Wulf et al 2008b ;Cuny et al 2009 ;Denis et al 2009 ;Krziwanek et al 2009 ;van Cleef et al 2010). La fréquence d'isolement de ST398 (SARM ou SASM) chez l'homme peut être faible, par exemple de l'ordre de 0,2 % aux Pays-Bas (van Belkum et al 2008) : cette étude ne montre pas de différence significative entre les souches isolées chez le porc et celles chez l'homme, que ce soit en situation de portage ou au contraire lors d'infections invasives ou locales (bacté-riémies, plaies ou urines infectées ou encore expectorations (figure 2).…”