Etiology of Cellulitis and Clinical Prediction of Streptococcal Disease: A Prospective Study

Abstract

Background. The importance of bacteria other than group A streptococci (GAS) in different clinical presentations of cellulitis is unclear, commonly leading to treatment with broad-spectrum antibiotics. The aim of this study was to describe the etiological and clinical spectrum of cellulitis and identify clinical features predicting streptococcal etiology. Methods. We prospectively enrolled 216 patients hospitalized with cellulitis. Clinical details were registered. Bacterial culture was performed from blood, cutaneous or subcutaneous tissue, and/or swabs from skin lesions. Paired serum samples were analyzed for anti-streptolysin O and anti-deoxyribonuclease B antibodies. Results. Serology or blood or tissue culture confirmed β-hemolytic streptococcal (BHS) etiology in 72% (146 of 203) of cases. An additional 13% (27 of 203) of cases had probable BHS infection, indicated by penicillin response or BHS cultured from skin swabs. β-hemolytic streptococcal etiology was predominant in all clinical subgroups, including patients without sharply demarcated erythema. β-hemolytic group C or G streptococci (GCS/GGS) were more commonly isolated than GAS (36 vs 22 cases). This predominance was found in the lower extremity infections. Group C or G streptococci in swabs were associated with seropositivity just as often as GAS. Staphylococcus aureus was cultured from swabs as a single pathogen in 24 cases, 14 (64%) of which had confirmed BHS etiology. Individual BHS-associated clinical characteristics increased the likelihood of confirmed BHS disease only slightly; positive likelihood ratios did not exceed 2.1. Conclusions. β-hemolytic streptococci were the dominating cause of cellulitis in all clinical subgroups and among cases with S aureus in cutaneous swabs. Group C or G streptococci were more frequently detected than GAS. No single clinical feature substantially increased the probability of confirmed BHS etiology.

Keywords: Streptococcus dysgalactiae subsp equisimilis; Streptococcus pyogenes; cellulitis; erysipelas; β-hemolytic streptococci.

Figure 1.

Flow chart of patient enrollment and evaluation for β-hemolytic streptococcal etiology. ^aOne case with Staphylococcus aureus in culture of normally sterile tissue and 2 positive (pos.) anti-streptolysin titers without significant rise were classified as negative (neg.) concerning confirmed β-hemolytic streptococcal (BHS) disease. ^bProportion with local clinical improvement at end of therapy among cases treated with penicillin only. Abbreviations: GAS, group A streptococcus; GBS, group B streptococcus; GCS/GGS, group C or G streptococcus.

Figure 2.

(A) Results of swab cultures of skin lesions in the affected body part. Coagulase-negative staphylococci, enterococci, and other bacteria interpreted as colonizers are not presented. Cases with Staphylococcus aureus found in addition to β-hemolytic streptococci (BHS) are not shown. This concerns 13 of 18 group A streptococcus (GAS) cases, 20 of 32 group C or G streptococcus (GCS/GGS) cases, and 4 of 8 group B streptococcus (GBS) cases. No Gram-negative bacteria were found in cases with BHS. (B) Seropositivity (see the Patients and Methods section) for streptococcal antibodies in relation to swab culture results. The number of cases (shown in parentheses) in each category of culture results is smaller than in A, because not all patients had 2 sets of serology. ^aThe anti-streptolysin O (ASO)-positive/anti-deoxyribonuclease B (ADB)-negative serological pattern was specific for GCS/GGS among cases with BHS in culture. The titer rise was not significantly lower in cases with this pattern from whom GCS/GGS were not cultured. (median log rise 0.40 vs 0.47, P = .369). ^bTwo of these cases also had growth of S aureus. ^cStaphylococcus aureus and/or Gram-negative bacteria found without other pathogens.