Overall bioburden by total colony count does not predict the presence of pathogens with high clinical relevance in hospital and community environments

Abstract

Background: Healthcare-associated infections (HAIs) affect millions of patients, increasing morbidity and mortality. Pathogens of HAIs originate from both the patient's own flora and the environment, including multi-drug-resistant organisms.

Aims: To determine the bioburden on different types of high-touch surfaces, and to identify cultures to species level and stratify strains into those of low and high clinical relevance.

Design: Association between bioburden and presence of pathogens of high clinical relevance (PHCR) in a tertiary care centre and urban environment.

Methods: The overall bioburden measured by total colony count (TCC) was assessed using tryptic soy agar contact plates and two selective agars to improve detection of PHCR. Isolates were routinely identified to species level using matrix-assisted laser desorption/ionization - time of flight mass spectrometry (MALDI-TOF). The definition of PHCR was based on listings outlined by the Centers for Disease Control and Prevention.

Findings: In total, 1431 contact plates were processed from 477 surfaces: 153 from hospitals and 324 from publicly accessible institutions or devices. At least one PHCR was identified from cultures from 73 samples. TCC was found to be poorly correlated with the presence of PHCR.

Conclusion: TCC poorly predicted the presence of PHCR, rendering the results from environmental sampling difficult to interpret. MALDI-TOF enables the identification of large numbers of isolates from the environment at low cost. Further studies on environmental contamination should use MALDI-TOF to identify all pathogens grown.

Keywords: Community; Hospital; MALDI-TOF; Pathogen; Surface contamination; Total colony count.