Sources of staphylococcal wound sepsis in surgical patients

Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

A six month prospective study was carried out in a surgical intensive care unit (SICU) of a university hospital to assess the incidence and routes of exogenous colonization by Staphylococcus aureus. A total of 157 patients were included in the study. One thousand one hundred and eleven specimens (nasal, surgical wound swabs, tracheal secretions obtained on admission and once a week thereafter, and all clinical specimens) were collected over a four month period from patients without nasal decontamination (A). They were compared with 729 specimens collected over a two month period from patients treated with nasal mupirocin ointment (B). All S. aureus strains were typed by restriction fragment length polymorphism (RFLP) pulsed-field gel electrophoresis after SmaI macrorestriction. The nasal colonization rates on admission were 25.5 and 32.7% in groups A and B, respectively. Thirty-one untreated patients (31.3%) and three patients (5.1%) treated with nasal ointment, acquired the nasal S. aureus in the SICU (P = 0.00027). Nasal carriers were more frequently colonized in the bronchopulmonary tract (Bp) and surgical wound (Sw) (62%) than patients who were not nasal carriers (14%) (P < 0.00001). The patterns were identical for nasal, Bp and Sw strains from the same patient. RFLP analysis characterized seven epidemic strains of methicillin-resistant S. aureus (MRSA) which colonized 60% of group A and 9% of group B patients (P < 0.00001). The bronchopulmonary tract infection rate was reduced in group B (P = 0.032). In conclusion, in an SICU, nasal carriage of S. aureus appeared to be the source of endogenous and cross-colonization. The use of nasal mupirocin ointment reduced the incidence of Bp and Sw colonization, as well as the MRSA infection rate.

Adherence of Staphylococcus aureus to cell monolayers

Adherence of four strains of Staphylococcus aureus to eukaryotic cell monolayers was assayed with [3H]-thymidine labelled bacterial cells and the results were analysed by non-parametric statistical tests. Adherence to primary (human mesothelial) and semi-continuous (human embryonic lung) cell monolayers was significantly better than to continuous cell lines (HEp2, HeLa and Vero). HEp2 cell monolayers provided the most reliable assay substrate of the continuous cell lines tested. Variation occurred between bacterial culture batches but the assay measured significant differences between adhesion levels of the strains and distinguished between high level (RN92, 8325-4) and low level (Wood46, ISP458) adhering strains. Adherence to different batches of cell monolayers also varied but relative adherence values for strains were similar and the ranking of strains according to adhesion values was unchanged. Potential adhesion mediators have been monitored for their effect on adhesion of a highly adherent strain (RN92) to HEp2 monolayers. Fibronectin, protein A and anti-protein A did not significantly affect adhesion. Lipoteichoic acid caused a significant inhibition of adhesion. With critical statistical analysis to accommodate inherent variations, this assay provides a useful model to study factors involved in adherence of Staph. aureus to eukaryotic cells.

A high incidence of bleeding is observed in a trial to determine whether addition of metronidazole is needed with latamoxef for prophylaxis in colorectal surgery

A prospective randomized trial has compared the use of latamoxef sodium (two doses) with latamoxef and metronidazole for elective colorectal surgery. The incidence of wound infection in patients receiving latamoxef alone was 34 per cent compared with 32 per cent in patients receiving latamoxef and metronidazole. Only eight of the 36 wound infections in this study could be classified as major. Only two patients developed an intra-abdominal abscess postoperatively and there was only one episode of septicaemia. Postoperative haemorrhage was recorded in 17 patients (15 per cent). Twelve episodes of bleeding occurred in the first 97 patients who entered the trial and prolongation of the prothrombin time was recorded in eight of 16 patients. In view of these findings 10 mg vitamin K was given with each dose of latamoxef to the last group of patients. However, bleeding occurred in five of 13 patients receiving vitamin K and entry to the study was therefore discontinued.

A comparison of pre-operative bathing with chlorhexidine-detergent and non-medicated soap in the prevention of wound infection

In a 60-week cross-over study on 5536 patients in 20 wards of three city hospitals (two general and one orthopaedic), pre-operative bathing with chlorhexidine-detergent failed to influence the incidence of postoperative infection, in spite of the relatively high incidence of infection with skin organisms. Of the patients bathing pre-operatively with chlorhexidine-detergent, 5.4 per cent subsequently became infected (4.0 per cent of clean wounds) and of those bathing with unmedicated soap 4.9 per cent (3.5 per cent of clean wounds). A single pre-operative bath with chlorhexidine-detergent would, therefore, appear to be of dubious value in preventing postoperative wound infection.