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

Abstract

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. The L. neglectus infestation of the orthopedic surgery, the ear-nose-throat clinics and the eye clinics 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 artificially Staphylococcus aureus colonization on the exoskeleton was assessed. 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 etiological 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 hours. Low colonization rates with etiologically relevant bacteria and rapid spontaneous decolonization in case of contamination make ant-borne transmissions to patients unlikely.