Detecting potential respiratory pathogens in the mouths of older people in hospital

Abstract

SIR—Hospital acquired pneumonia (HAP) is the third most common health care associated infection, and complicates 1.27% of UK hospital admissions [1]. The incidence is higher in groups such as the elderly, post-operative patients and those on specialist units such as liver, burns or haematology [1]. The incidence of HAP appears to increase with age [2], and the mortality in older people is thought to be between 12.2–55% depending on the group studied [3, 4]. The bacteria which cause hospital acquired pneumonia (HAP) such as Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus are thought to reside in the oropharynx before being aspirated into the lungs causing pneumonia [5, 6]. These bacteria are more commonly found in the mouths of sick or institutionalised persons than healthy people [7–11] but are not considered part of the normal oral flora. Randomised controlled trials employing rigorous oral hygiene interventions have significantly reduced the incidence of HAP in both nursing home residents [12] and ventilated persons undergoing cardiothoracic surgery [13], but these studies have not identified exactly why oral hygiene may be beneficial. It has been hypothesised that heavy dental plaque load, prior antibiotics or illness may allow these ‘foreign’ bacteria to become part of the oral bacterial community. Currently the relationship between plaque, oral bacteria and HAP is unclear. The next step is to investigate whether prior oral bacterial colonisation with hospital pneumonia pathogens is associated with subsequent HAP. However, the most sensitive oral sampling site for gram-negative bacilli and S. aureus need to be verified before this research can be undertaken. In particular clarification is needed regarding the utility of dental or denture plaque as a site for identifying these bacteria. The aims of this study were to identify the optimal sampling method for identifying gram negative bacilli and S. aureus in the mouth which could cause HAP, and to explore the extent to which visible dental plaque and the number of days on antibiotics contributed to the emergence of these bacteria.