Staphylococcus aureus (or Staph. aureus) is a bacterium that lives harmlessly on the skin. However, Staph. aureus can also cause infections, particularly in hospitalised patients. Hospital staff work hard to prevent patients from developing Staph aureus infections. They do this in a number of ways including regularly washing their hands, wearing protective clothing (gloves and aprons) and cleaning the hospital environment. Despite these measures patients continue to pick up Staph. aureus infection in hospital.
To understand why this happens we investigated how patients acquire Staph. aureus in hospital. We used a new technique called whole-genome sequencing (WGS). WGS allows us to read a bacterium’s genetic code (the DNA) and compare codes from different bacteria to see how closely related they are and detect when someone has caught an infection from someone else. We looked in detail at nurses, doctors, the environment, and patients in a critical care ward. We found that many doctors and nurses carry Staph. aureus and that the ward environment is contaminated with these bacteria. We also found that patients appeared to be picking up Staph. aureus whilst on the ward. However, when we looked at where Staph. aureus was actually coming from our results were surprising. On the critical care ward there was very little transmission from staff, patients and the ward environment. This strongly suggests that the measures used by hospital staff to prevent spread of Staph aureus actually work rather well.
Despite this it appeared as though patients were still catching Staph. aureus. This could be because patients already had Staph. aureus when they arrived on the ward but we missed it because we were testing the wrong parts of the body or because the patients had had antibiotics or had been washed with antibacterial soap. We will investigate this in future work.