The authors base their findings on a study of 98 critically ill patients in intensive care who required mechanical help with their breathing for more than 48 hours. The patients were drawn from medical and surgical specialties.
Levels of glucose were measured in their blood samples and lung secretions (bronchial aspirates). The lung secretions were also routinely tested twice weekly, or whenever an infection was suspected, for the presence of harmful bacteria, including methicillin resistant Staphylococcus aureus (MRSA).
Glucose was found in the bronchial aspirates of 58 of the 98 patients, and blood glucose levels in these patients also tended to be higher than those of patients with no glucose in their aspirates. Fifteen of the patients were diabetic.
The aspirates of 87 patients were tested for the presence of harmful bacteria. Aspirates containing glucose were also twice as likely to contain harmful bacteria, and twice as likely to contain MRSA, as those with no detectable glucose.
Patients with MRSA spent seven days longer in intensive care, had higher levels of an inflammatory marker (C reactive protein), and evidence of inflammation on their chest X rays than those in whom MRSA was not found. This suggests that they were more than just carriers of the bacteria, say the authors.
In most cases, the detection of glucose preceded MRSA, suggesting that glucose could have either caused or promoted growth of the bacteria, they add.
Staphylococcus aureus goes through a period of rapid growth during which it uses supplies of glucose. And glucose may also interfere with local immune responses in the airway.
An accompanying editorial suggests that a link between an increased risk of infection and abnormally high levels of glucose is biologically plausible. Too much glucose also tends to give immune cells the equivalent of a "hangover."
But the author cautions that further research will be needed to confirm whether an increase in glucose levels in lung secretions boosts the risk of infection, and whether lowering these levels will cut the risk of infection with harmful bacteria, including MRSA.