A comparison of prophylactic antibiotic regimens against airborne orthopaedic wound contamination.

Deep infection remains a major complication of joint replacement surgery despite advances in theatre design, surgical technique and antibiotic prophylaxis. Major randomized controlled trials to determine the most effective antibiotic prophylaxis are difficult to construct and interpret. In a conventional theatre, most orthopaedic intra-operative wound contamination arrives by the airborne route. This paper describes a unique method used to compare antibiotics against airborne bacteria. Seven antibiotics were incorporated into blood agar at concentrations equivalent to serum levels. Plates were then exposed to airborne theatre bacteria using a multiple synchronous collection technique. After incubation, the percentage kill was calculated for each antibiotic. At concentrations equivalent to serum level 1h post i.v. dose, all the antibiotics proved highly effective, with kill rates > 95%. Imipenem and co-amoxiclav significantly outperformed the other antibiotics with kill rates of 99.6% and 99.4%, respectively. At trough levels, the antibiotics achieved kill rates from 61% to 97.6%. Future randomized controlled trials comparing large numbers of antibiotics in the setting of an already low infection rate are inappropriate. This technique for comparing antibiotic prophylaxis in quick, inexpensive and repeatable. The superiority of imipenem is not unexpected, but of more interest is the effectiveness of co-amoxiclav over the presently favoured cefuroxime.

Nursing staff workload as a determinant of methicillin-resistant Staphylococcus aureus spread in an adult intensive therapy unit.

Acquisition of methicillin resistant Staphylococcus aureus (MRSA) in the intensive care unit of a tertiary referral centre was monitored over a 19-month period. The incidence of new cases of MRSA correlated with peaks of nursing staff workload and times of reduced nurse/patient ratios within the unit. This implies that nurse understaffing contributes significantly to the spread of MRSA in an ITU setting.

Evaluation of new streptococcal latex grouping kit.

AIMS: To evaluate a new streptococcal latex grouping kit (Shield Diagnostics Ltd) and compare it against an established latex agglutination method (Streptex; Wellcome Diagnostics). METHODS: Two hundred and forty seven strains of streptococci and enterococci were tested with each kit by one operator and according to the manufacturer's instructions. Strains failing to group or giving discordant results were identified to species level. RESULTS: Two discrepant grouping results were observed and 13 non-beta haemolytic streptococci failed to group with either product. The Shield kit successfully identified 232 isolates at 15 minutes of enzyme extraction incubation compared with 224 and 233 on short (15 minutes) and long (1 hour) incubations, respectively, for Streptex (p > 0.23 for both comparisons). On short incubation only, the Shield kit detected significantly more strains of Enterococcus faecium (p = 0.007). The reaction strengths were similar for both kits (p > 0.16). No cross-reactions were observed but the Streptex kit produced significantly fewer tests with visible granularity (p < 0.003). CONCLUSIONS: Although the Shield product appeared to detect group D antigen more readily, overall no important differences in performance were observed. Prospective users of the new method should first become familiar with its characteristics.