Author: Ho, Jeffery
Title: Characterisation of nasal colonization and hand contamination of food handlers with Staphylococcus aureus and investigation of virulence and resistance determinants of isolates
Degree: Ph.D.
Year: 2015
Subject: Food handling -- China -- Hong Kong -- Health aspects
Food service -- Sanitation -- China -- Hong Kong
Staphylococcus aureus infections -- China -- Hong Kong
Hong Kong Polytechnic University -- Dissertations
Department: School of Nursing
Pages: x, 331 pages : illustrations
Language: English
Abstract: Investigation of staphylococcal food poisoning (SFP) outbreaks has frequently detected the same clone of Staphylococcus aureus from food handlers and the incriminated food, emphasising that S. aureus colonization of food handlers is of public health significance. This study aimed to investigate nasal colonization and hand contamination rates with Staphylococcus aureus in food handlers employed in large scale catering establishments in Hong Kong over a ten year period. This was achieved by means of three related cross sectional studies, conducted before and after SARS, and in 2011. Risk factors for colonisation and temporal changes of prevalence of SE/ SEl genes circulating in S. aureus strains nasally colonizing food handlers were determined. Strains were characterised by spa typing to determine carriage status and track the route of transmission between workers in food establishments. The prevalence of qac genes in nasal isolates was investigated to determine if increased use of disinfectants in food establishments had selected for disinfectant tolerant strains. Nasal swabs and hand imprint specimens were collected from food handlers working in large catering establishments in 2011 and isolates compared with those collected in the earlier studies. Risk factors were investigated by means of validated questionnaires completed in 2002 and 2011 and analysed by multivariate analysis. Staphylococcal enterotoxins (SE), spa, and antibiotic- and antiseptic-resistance genes were detected by PCR amplification followed by sequencing as appropriate. Tracking of colonisation status and transmission to hands was performed by examination of spa types. Susceptibility to antibiotics was performed by disk diffusion and to antiseptics by determination of minimum inhibitory and bactericidal concentrations. Association between presence of SE genes, qac genes, antibiotic resistance, and spa types was investigated.
This study revealed that the prevalence of nasal colonisation and hand contamination with S. aureus in food handlers was significantly reduced after the SARS epidemic and the reduction appears to have been sustainable. There was a significant association between handling of raw meat and nasal carriage of S. aureus which was supported by the presence of specific clones previously associated with raw meat. Prevalence rates of classical SE genes remained stable while novel types varied over time. The prevalence of qac genes appeared to increase over time although this did not reach statistical significance and was found to be associated with the use of quaternary ammonium compound-containing disinfectants. The majority of hand contamination appeared to be attributable to cross-contamination from other persistently colonized co-workers. The sustained reduction in nasal colonisation and the remarkable decrease in hand contamination rates over time emphasises the importance of hygiene campaigns in reducing spread of infectious agents. The higher colonization rate in raw meat handlers indicates that exposure to raw meat may increase infection risk. The frequent presence of SE- and qac genes in nasal isolates underscores the toxigenic potential of these strains and their ability to persist in the environment respectively. This suggests that correct performance of environmental cleaning is an essential element in prevention of transmission and, when combined with efficient hand washing, could reduce transient nasal colonisation and hand contamination and thereby, the incidence of staphylococcal food poisoning.
Access: open access

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