Early identification of patients at high risk of group A streptococcus-associated necrotizing skin and soft tissue infections: a retrospective cohort study

Severe skin infections

PURPOSE OF REVIEW

The incidence of necrotizing soft-tissue infections (NSTI) has increased during recent decades. These infections are still associated with high morbidity and mortality, underlining a need for continued education of the medical community. This review will focus on practical approaches to management of NSTI focusing on antibiotic therapies and optimizing the management of group A streptococcus (GAS)-associated NSTIs.

RECENT FINDINGS

Antibiotic therapy for NSTI patients faces several challenges as the rapid progression of NSTIs mandates broad-spectrum agents with bactericidal action. Current recommendations support using clindamycin in combination with penicillin in case of GAS-documented NSTIs. Linezolide could be an alternative in case of clindamycin resistance.

SUMMARY

Reducing the time to diagnosis and first surgical debridement, initiating early broad-spectrum antibiotics and early referral to specialized centres are the key modifiable factors that may impact the prognosis of NSTIs. Causative organisms vary widely according to the topography of the infection, underlying conditions, and geographic location. Approximately one third of NSTIs are monomicrobial, involving mainly GAS or Staphylococcus aureus . Data for antibiotic treatment specifically for necrotizing soft-tissue infections are scarce, with guidelines mainly based on expert consensus.

Necrotizing soft tissue infections in critically ill neutropenic patients: a French multicentre retrospective cohort study

BACKGROUND

Necrotizing soft tissue infections (NSTIs) are rare life-threatening bacterial infections. Few data are available regarding neutropenic patients with NSTIs. Our objectives were to describe the characteristics and management of neutropenic patients with NSTIs in intensive care units (ICUs). We conducted a retrospective multicentre cohort study in 18 ICUs between 2011 and 2021. Patients admitted with NSTIs and concomitant neutropenia at diagnosis were included and compared to non-neutropenic patients with NSTIs. The relationship between therapeutic interventions and outcomes was assessed using Cox regression and propensity score matching.

RESULTS

76 neutropenic patients were included and compared to 165 non-neutropenic patients. Neutropenic patients were younger (54 ± 14 vs 60 ± 13 years, p = 0.002) and had less lower limb (44.7% vs 70.9%, p < 0.001) and more abdomino-perineal NSTIs (43.4% vs 18.8%, p < 0.001). Enterobacterales and non-fermenting gram-negative bacteria were the most frequently isolated microorganisms in neutropenic patients. In-hospital mortality was significantly higher in neutropenic than in non-neutropenic patients (57.9% vs 28.5%, p < 0.001). Granulocyte colony-stimulating factor (G-CSF) administration was associated with a lower risk of in-hospital mortality in univariable Cox (hazard ratio (HR) = 0.43 95% confidence interval (CI) [0.23-0.82], p = 0.010) and multivariable Cox (adjusted HR = 0.46 95% CI [0.22-0.94], p = 0.033) analyses and after overlap propensity score weighting (odds ratio = 0.25 95% CI [0.09; 0.68], p = 0.006).

CONCLUSIONS

Critically ill neutropenic patients with NSTIs present different clinical and microbiological characteristics and are associated with a higher hospital mortality than non-neutropenic patients. G-CSF administration was associated with hospital survival.

Impact of prior antibiotic therapy on severe necrotizing soft-tissue infections in ICU patients: results from a French retrospective and observational study

Necrotizing soft-tissue infection (NSTI) is a life-threatening pathology that often requires management in intensive care unit (ICU). Therapies consist of early diagnosis, adequate surgical source control, and antimicrobial therapy. Whereas guidelines underline the need for appropriate routine microbiological cultures before starting antimicrobial therapy in patients with suspected sepsis or septic shock, delaying adequate therapy also strongly increases mortality. The aim of the present study was to compare the characteristics and outcomes of patients hospitalized in ICU for NSTI according to their antimicrobial therapy exposure > 24 h before surgery (called the exposed group) or not (called the unexposed group) before surgical microbiological sampling. We retrospectively included 100 consecutive patients admitted for severe NSTI. The exposed group consisted of 23(23%) patients, while 77(77%) patients belonged to the unexposed group. The demographic and underlying disease conditions were similar between the two groups. Microbiological cultures of surgical samples were positive in 84 patients and negative in 16 patients, including 3/23 (13%) patients and 13/77 (17%) patients in the exposed and unexposed groups, respectively (p = 0.70). The distribution of microorganisms was comparable between the two groups. The main antimicrobial regimens for empiric therapy were also similar, and the proportions of adequacy were comparable (n = 60 (84.5%) in the unexposed group vs. n = 19 (86.4%) in the exposed group, p = 0.482). ICU and hospital lengths of stay and mortality rates were similar between the two groups. In conclusion, in a population of severe ICU NSTI patients, antibiotic exposure before sampling did not impact either culture sample positivity or microbiological findings.

Antibiotics in Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections (NSTIs) are rare life-threatening bacterial infections characterized by an extensive necrosis of skin and subcutaneous tissues. Initial urgent management of NSTIs relies on broad-spectrum antibiotic therapy, rapid surgical debridement of all infected tissues and, when present, treatment of associated organ failures in the intensive care unit. Antibiotic therapy for NSTI patients faces several challenges and should (1) carry broad-spectrum activity against gram-positive and gram-negative pathogens because of frequent polymicrobial infections, considering extended coverage for multidrug resistance in selected cases. In practice, a broad-spectrum beta-lactam antibiotic (e.g., piperacillin-tazobactam) is the mainstay of empirical therapy; (2) decrease toxin production, typically using a clindamycin combination, mainly in proven or suspected group A streptococcus infections; and (3) achieve the best possible tissue diffusion with regards to impaired regional perfusion, tissue necrosis, and pharmacokinetic and pharmacodynamic alterations. The best duration of antibiotic treatment has not been well established and is generally comprised between 7 and 15 days. This article reviews the currently available knowledge regarding antibiotic use in NSTIs.

Beta-Hemolytic Streptococci and Necrotizing Soft Tissue Infections

β-hemolytic streptococci are major causes of necrotizing soft tissue infections (NSTIs), Streptococcus pyogenes (group A streptococcus; GAS) in particular. NSTIs caused by Streptococcus dysgalactiae (SD) have also been reported. In the INFECT cohort of 409 NSTIs patients, more than a third of the cases were caused by GAS (31%) or SD (7%). Risk factors of streptococcal NSTIs compared to streptococcal cellulitis have previously been largely unknown. The INFECT study confirmed blunt trauma as an important risk factor. In addition, absence of pre-existing skin lesions and a lower BMI were associated with NSTIs. The study also confirmed that septic shock is more frequent in GAS cases than in other types of NSTIs. Septic shock was also among several predictors of mortality. The role of intravenous immunoglobulin (IVIG) in streptococcal NSTIs has been unclear. In the INFECT cohort, IVIG treatment was associated with increased survival. As in other studies, a significant microbial diversity was observed, but with predominance of a few emm types. Overall, the INFECT study gives a comprehensive and contemporary picture of the clinical characteristics and the microbes involved in streptococcal NSTIs. The reported severity of disease underscores the need for new efforts aimed at identifying novel diagnostic measures and improved treatment.