Risk assessment of the mechanical spread of bacterial pathogens due to Lasius neglectus ants infesting a tertiary hospital.

Introduction: Mechanical spread of microbial pathogens has been investigated in cockroaches, but less well in ants. Considerably less information is available for ants. An investigation into ant-borne mechanical pathogen transmission was triggered by an infestation of a tertiary care hospital with Lasius neglectus ants.
Methods: The L. neglectus infestation of the orthopaedic surgery department, the ear-nose-throat clinic and the eye clinic as well as of outdoor areas was monitored and correlated with seasonal and weather influences. Microbial colonization on the ants' exoskeleton as well as in homogenates of complete insects and decolonization dynamics of artificial Staphylococcus aureus colonization on the exoskeleton was assessed.
Results: In a low-level infestation setting, L. neglectus activity showed seasonal variations and was positively correlated with temperature (r = 0.7515; P=0.0368) but not with precipitation (r = 0.4699, P=0.2431). Colonization with environmental commensals dominated, while exoskeleton colonization with bacteria with potential aetiological relevance for nosocomial infections was higher for ants from the inpatient setting (6%) than from outdoor areas (0%). Artificial colonization of the exoskeleton with S. aureus vanished to values statistically indistinguishable from baseline within 72 h.
Conclusions: Low colonization rates with aetiologically relevant bacteria and rapid spontaneous decolonization in the case of contamination make ant-borne transmissions to patients unlikely.
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