High isolation rate of Staphylococcus aureus from surgical site infections in an Indian hospital

Abstract

Sir, Surgical site infection (SSI) is a major source of morbidity and mortality and is an important outcome indicator after surgery.1 SSIs are the second most frequent nosocomial infection in the general hospital population.1 A study showed that subjects who develop SSI were five times more likely to be re-admitted and re-operated on than those without infection and were also reported to be twice as likely to die during the post-operative period.1 Few studies of the incidence and causes of SSI and its prevention have been conducted in resource-limited countries. Furthermore, isolation and antibiogram profiles require periodical monitoring, especially in settings like India, where SSIs account for considerable morbidity and mortality rates. We evaluated the aetiological agents of SSI and their resistance patterns at a city government hospital in Chennai, southern India during a 6 month period from January to June 2003. Ethic committee approval was obtained from the University of Madras for conducting the study. Subjects were classified as having an SSI when there was a skin eruption or purulent drainage at the surgical-site incision, positive for bacteria by culture of material obtained by aseptic means within 60 days of a surgical procedure and inflammatory signs such as pain, tenderness, localized swelling, redness and/or heat. As per the criteria, a total of 52 wound specimens of post-SSIs were analysed. Culture materials collected by washing the wound with sterile saline and applying sterile cotton swabs (Himedia, Mumbai, India) were transported on Cary & Blair media in a 0° mini cooler (Tarson, Mumbai, India), cultured and identified using standard bacteriological procedures.2 Antibiotic susceptibility testing was performed using the conventional Kirby–Bauer disc diffusion test (CLSI, formerly NCCLS).3 Sixty-two bacterial isolates were obtained on 52 cultures and 6 were declared bacteriologically sterile. Single isolates were seen in 31 (59.6%) and multiple isolates in 15 (28.8%) instances. Gram-negative bacteria predominated with (n = 36) 58%, followed by (n = 26) 41.9% Gram-positive isolates. The most common bacteria were Staphylococcus aureus (n = 23; 37%) and Pseudomonas aeruginosa (n = 23; 37%), followed by Klebsiella pneumoniae (n = 5; 8%), Acinetobacter spp. (n = 2; 3.2%), Proteus spp. (n = 3; 4.8%), Escherichia coli (n = 2; 4.8%), Citrobacter freundii (n = 1; 1.6%), Edwardsiella tarda (n = 1; 1.6%) and Enterococcus faecalis (n = 1; 1.6%). The antibiogram pattern of the isolates tested is shown in Table 1. One of the most prevalent bacteria was S. aureus (37%) that comprised five (21.7%) methicillin-resistant S. aureus (MRSA). MRSA infections are of great concern due to their higher morbidity and mortality rates.4–6 Fortunately, all of the MRSA isolates in our study were susceptible to vancomycin (30 µg/disc). The other major concern in SSIs is S. aureus that is believed to originate from the patient's own anterior nares. Randomized trials advocate the use of topical intranasal mupirocin ointment to effectively eradicate Staphylococcus species and more importantly S. aureus from the anterior nares soon after treatment. Furthermore, complete eradication is believed to be achieved with as little as one dose. The increased isolation rates of S. aureus stress the need to screen and treat subjects for pre-operative nasal carriage of the pathogen using topical mupirocin, which could possibly influence the aetiology of SSIs. In a study that enrolled 104 subjects with SSIs, S. aureus was predominant with 38% MRSA,4 which concurs with our findings. Another Indian study has reported the preponderance of S. aureus (with 38.56% MRSA) followed by E. coli and Pseudomonas spp. from surgical wounds. The study suggests that the absence of SSI could be an important part of the successful outcome of any operative procedure. Strict measures to reduce the detection of colonizing bacteria from the infection sites need to be ensured, and therefore culture material needs to be collected always from the deeper part of the superficial incision site, washed prior to collection with sterile saline. We suggest that the maintenance of S. aureus control strategies should be the need of the hour in Indian settings. The high prevalence of P. aeruginosa in our study may be due to the fact that it can survive well in moist environments, often causing severe tissue damage due to its invasiveness. Susceptibility of the Gram-negative and -positive bacterial isolates from SSIsa an refers to the number of isolates tested. Results shown in the table are the numbers of susceptible isolates with percentages of isolates given in parentheses. NT refers to susceptibility not tested. Susceptibility of the Gram-negative and -positive bacterial isolates from SSIsa an refers to the number of isolates tested. Results shown in the table are the numbers of susceptible isolates with percentages of isolates given in parentheses. NT refers to suscepti