Background: Cellulitis is a common infection at our center. Broad-spectrum antibiotic or antibiotic combination is often prescribed for most adult patients with cellulitis. A contributing factor to the high prevalence of broad-spectrum antibiotic or antibiotic combination for cellulitis is the lack of data specific to the epidemiology and microbiology of cellulitis in Thai patients.

Objective: To determine the characteristics of patients with cellulitis, the prevalence of causative bacteria and their antibiotic susceptibility, antibiotic treatment, and clinical outcomes of cellulitis in adult patients at Siriraj Hospital.

Materials and Methods: The retrospective study included patients aged 18 years and older with a diagnosis of cellulitis who received medical care at Siriraj Hospital between June and December 2016. Collected data included demographic information, underlying conditions, type(s) of infection, location(s) of cellulitis, clinical features of cellulitis, culture and antibiotic susceptibility results, antibiotic prescriptions, and clinical outcomes of cellulitis.

Results: Of the 970 adult cellulitis patients included, 20.6% were hospitalized and 79.4% were outpatients. The mean age of patients was 60.6±18.5 years, 75.4% had at least one underlying illness, and 55% were females. Eighty-six percent of patients had community-acquired infection. Amoxicillin-clavulanate, dicloxacillin, ceftriaxone plus clindamycin, and ceftriaxone alone were the most commonly prescribed antibiotics. Ninety-seven percent of patients had a favorable clinical outcome. The overall mortality rate was 2.0%, and the cellulitis-related mortality rate was 0.3%. Hospitalized patients had a significantly lower proportion of favorable clinical outcome than ambulatory patients. The most commonly isolated bacteria (73.7%) were Grampositive bacteria (beta-hemolytic streptococci or Staphylococcus aureus). Antibiotic combination therapy was significantly more prevalent among hospitalized patients. Patients who received antibiotic combination had a significantly less favorable outcome than those who received monotherapy.

Conclusion: Seventy-seven percent of adult patients with cellulitis at Siriraj Hospital received broad-spectrum antibiotic or antibiotic combination despite the most commonly isolated bacteria being beta-hemolytic streptococci and methicillin-susceptible S. aureus (MSSA), both of which are normally treatable with a simple narrow-spectrum antibiotic. Mortality and complication rates in cellulitis were very low. Appropriate antibiotic treatment of cellulitis at Siriraj Hospital should be encouraged.

Keywords: Thailand, Epidemiology, Cellulitis, Bacteria, Antibiotic