Bacterial skin infections at a tertiary dermatological centre

Bacterial skin infections are common clinical problems encountered in most fields of clinical medicine. Staphylococcus aureus and group A streptococci are common invaders of eczematous, traumatised or immunocompromised skin. Advances in pharmacology have introduced a wide array of new antibiotics into the physician's armamentarium, but the rising incidence of bacterial resistance continues to be a problem. A retrospective study was carried out on 331 patients at the National Skin Centre, Singapore, to establish the causes of common primary and secondary pyodermas, as well as to determine the antibiotic sensitivities of the microorganisms responsible.

A retrospective study of the medical records of 331 patients seen at the Centre for skin infections between October 1995 and May 1996 was done. Skin cultures and antibiotic sensitivity testing was carried out and the data analysed. Both primary pyodermas (impetigo, folliculitis, furuncles/carbuncles and cellulitis) and secondary pyodermas (infected ulcers and infected eczemas) were included. The results of bacterial isolation cultures and sensitivity of the organisms isolated to the commonly used antibiotics such as cloxacillin, penicillin, erythromycin and the tetracyclines were analysed.

Staphylococcus aureus was the commonest organism isolated from both primary and secondary pyodermas, accounting for 67% and 46.7% of the organisms isolated, respectively. There was no significant difference in the racial representation in each of the various skin infections, but there was a significantly greater female representation in the infected ulcers. The secondary pyodermas had a significantly higher incidence of gram negative organisms causing infections, as well as culture results showing multiple bacterial pathogens. The methicillin resistant strains of S. aureus were commoner in the secondary pyodermas, and accounted for 4.2% of the total organisms isolated and 7% of the total strains of S. aureus. The S. aureus had a high rate of resistance (89.5%) to penicillin and ampicillin, but was very sensitive (93%) to cloxacillin, cephalexin and cotrimoxazole. The incidence of erythromycin resistance was 18.7%.

In patients with primary pyodermas, cloxacillin should be the first line antibiotic used, with erythromycin as a useful but less preferred alternative. The favoured combination of ampicillin and cloxacillin has little place in routine treatment of skin infections, except for cellulitis and infected eczemas. A cephalosporin can also be used in these conditions if single drug therapy is desired. The secondarily infected ulcers are difficult to treat and would probably require the use of combination therapy in view of frequent mixed infections.