Background: The consequences of infection with Staphylococcus aureus can be severe, so strategies for prevention are important. We examined S. aureus isolates from blood and from nasal specimens to determine whether the organisms in the bloodstream originated from the patient's own flora.
Methods: In a multicenter study, swabs for culture were obtained from the anterior nares of 219 patients with S. aureus bacteremia. A total of 723 isolates were collected and genotyped. In a second study, 1640 S. aureus isolates from nasal swabs were collected over a period of five years and then compared with isolates from the blood of patients who subsequently had S. aureus bacteremia.
Results: In the multicenter study of S. aureus bacteremia, the blood isolates were identical to those from the anterior nares in 180 of 219 patients (82.2 percent). In the second study, 14 of 1278 patients who had nasal colonization with S. aureus subsequently had S. aureus bacteremia. In 12 of these 14 patients (86 percent), the isolates obtained from the nares were clonally identical to the isolates obtained from blood 1 day to 14 months later.
Conclusions: A substantial proportion of cases of S. aureus bacteremia appear to be of endogenous origin since they originate from colonies in the nasal mucosa. These results provide support for strategies to prevent systemic S. aureus infections by eliminating nasal carriage of S. aureus.