Immune cell subsets in necrotizing fasciitis: an immunohistochemical analysis

Regional Variations in Microbiology and Outcomes of Necrotizing Soft Tissue Infections: A Systematic Review and Meta-Analysis

Background: Frequency, microbiology, and outcomes of necrotizing soft tissue infections (NSTIs) could vary across the United States because of differences in locoregional and environmental factors. We synthesized the literature from across the regions of the United States on NSTIs in a systematic review/meta-analysis. Methods: PubMed, ProQuest, Scopus, and Web of Science databases were systematically searched and screened. DerSimonian-Laird random-effects meta-analyses were performed using 'meta' package in R to determine pooled prevalences. Meta-regression analyses examined moderator effects of risk factors. Results: Twenty-seven studies (2,242 total patients) were included. Pooled prevalences of polymicrobial and monomicrobial infections were 52.2% and 39.9%, respectively. The prevalence of monomicrobial NSTIs increased over the last two decades (p = 0.018), whereas polymicrobial infections declined (p = 0.003). Meta-regression analysis showed that most polymicrobial NSTIs were Fournier gangrene (p < 0.001), whereas monomicrobial NSTIs mostly affected extremities (p < 0.001). Staphylococcus aureus was the most common organism isolated (predominantly in the South), followed by Bacteroides spp. (predominately in the East) and Streptococcus pyogenes. Methicillin-resistant Staphylococcus aureus (MRSA) accounted for 11.9% of NSTIs, mainly in the South. The overall mortality rate was 17.8% and declined over last two decades (p < 0.001), with the lowest rate reported in the last decade at 13% without any regional differences. Conclusions: Advancement in the management of NSTIs may have contributed to the observed decline in NSTI-related mortality in the United States. However, the proportion of monomicrobial NSTIs seems to be increasing, possibly because of increased comorbidities affecting extremities. Causative organisms varied by region. Multi-center observational studies are warranted to confirm our observations.

Periocular necrotizing soft tissue infection in Greater Copenhagen

PURPOSE

Necrotizing soft tissue infection, also known as necrotizing fasciitis (NF), is a fast-spreading life-threatening infection that most commonly affects the lower limbs, groin, or abdomen. Periocular necrotizing fasciitis (PNF) is rare. Limited data exist on PNF immune cell subset; hence, this study aims to determine the representation of immune cell subsets in patients diagnosed with PNF using immunohistochemical stainings.

METHODS

All patients diagnosed with PNF at Copenhagen University Hospital from 2008 to 2018 were included. Their electronic medical records and pathology reports were assessed, and available tissue specimens were reviewed and stained with monoclonal antibodies for CD1a⁺ Langerhans' cells, CD3⁺ T lymphocytes, CD15⁺ granulocytes, CD44⁺ lymphohematopoietic cells, CD68⁺ histiocytes, CD79α⁺ B lymphocytes, and FXIIIa+ dendritic macrophages and Langerhans' cells. The number of positive cells was counted, and an average score was calculated. The location of immune cells and bacteria was assessed.

RESULTS

The specimens were characterized by acute inflammation and necrosis of the fascia, while striated muscle involvement was less frequent. Haemolytic group A streptococci and Staphylococcus aureus were identified and mainly located in the deep dermis and subcutis in close relation to the fascia. Only few areas harboured both bacteria and inflammatory cells. Granulocytes, histiocytes and CD44⁺ lymphohematopoietic cells were demonstrated to be abundant in all patients, while B and T lymphocytes, dendritic macrophages and Langerhans' cells were less frequent.

CONCLUSION

The immune cell subsets found in this study of PNF were consistent with those identified in the literature on NF in other anatomical locations. This study concludes that immune cells are abundant and exhibit a typical pattern in PNF.

Exhaustion of the immune system by Group A Streptococcus necrotizing fasciitis: the occurrence of late secondary infections in a retrospective study

BACKGROUND

Necrotizing fasciitis is a potentially lethal condition for which early and adequate treatment with surgical debridement and broad-spectrum intravenous antibiotics are essential for survival. It is hypothesized that Group A Streptococcus (GAS) necrotizing fasciitis causes exhaustion of the immune system, making these patients more susceptible for late secondary infections.

METHODS

A retrospective study was conducted of all patients with necrotizing fasciitis between 2002 and 2016. Patients with necrotizing fasciitis based on macroscopic findings, positive Gram staining, culture or fresh frozen section of fascia biopsies were included. Patients with necrotizing fasciitis were divided into two groups based on the presence of GAS. Of both groups, clinical course, outcome and occurrence of late secondary infections were analyzed. For the occurrence of secondary infections, pneumonia was chosen as reference for late secondary infections.

RESULTS

Eighty-one patients with necrotizing fasciitis were included of which 38 (47%) had GAS necrotizing fasciitis and 43 (53%) had non-GAS necrotizing fasciitis. Patients with GAS necrotizing fasciitis were younger (50 vs. 61 years, p=0.023) and more often classified as ASA I (45% vs. 14%, p=0.002) compared with patients with non-GAS necrotizing fasciitis. In-hospital mortality rate for necrotizing fasciitis was 32%. Patients with comorbidities were more likely to die of necrotizing fasciitis compared with patients without comorbidities (OR 7.41, 95% CI 1.58 to 34.63). Twelve patients (39%) with GAS necrotizing fasciitis developed pneumonia compared with four patients (13%) with non-GAS necrotizing fasciitis (p=0.017; OR 4.42, 95% CI 1.124 to 15.79). Median time from diagnosis to development of pneumonia in patients with GAS necrotizing fasciitis was 10 days (IQR 9).

CONCLUSION

Patients with GAS necrotizing fasciitis have an increased risk to develop late secondary infections during initial treatment for necrotizing fasciitis compared with patients with necrotizing fasciitis without involvement of GAS. This suggests exhaustion of the immune system after severe GAS infection.

LEVEL OF EVIDENCE

III.

Cholesterol-dependent cytolysins impair pro-inflammatory macrophage responses

Necrotizing soft tissue infections are lethal polymicrobial infections. Two key microbes that cause necrotizing soft tissue infections are Streptococcus pyogenes and Clostridium perfringens. These pathogens evade innate immunity using multiple virulence factors, including cholesterol-dependent cytolysins (CDCs). CDCs are resisted by mammalian cells through the sequestration and shedding of pores during intrinsic membrane repair. One hypothesis is that vesicle shedding promotes immune evasion by concomitantly eliminating key signaling proteins present in cholesterol-rich microdomains. To test this hypothesis, murine macrophages were challenged with sublytic CDC doses. CDCs suppressed LPS or IFNγ-stimulated TNFα production and CD69 and CD86 surface expression. This suppression was cell intrinsic. Two membrane repair pathways, patch repair and intrinsic repair, might mediate TNFα suppression. However, patch repair did not correlate with TNFα suppression. Intrinsic repair partially contributed to macrophage dysfunction because TLR4 and the IFNγR were partially shed following CDC challenge. Intrinsic repair was not sufficient for suppression, because pore formation was also required. These findings suggest that even when CDCs fail to kill cells, they may impair innate immune signaling responses dependent on cholesterol-rich microdomains. This is one potential mechanism to explain the lethality of S. pyogenes and C. perfringens during necrotizing soft tissue infections.

[Necrotizing fasciitis. 2011 update]

Necrotizing fasciitis belongs to a group of complicated soft tissue infections that can be even life threatening. Despite growing knowledge about its etiology, predictors, and the clinical progression, the mortality remains at a high level with 20%. A relevant reduction can be achieved only by an early diagnosis followed by consistent therapy. The clinical findings in about 75% of the cases are pain out of proportion, edema and tenderness, blisters, and erythema. It is elementary to differentiate a necrotizing or a non-necrotizing soft tissue infection early. In uncertain cases it can be necessary to perform a surgical exploration to confirm the diagnosis. The histopathologic characteristics are the fascial necrosis, vasculitis, thrombosis of perforating veins, the presence of the disease-causing bacteria as well as inflammatory cells like macrophages and polymorphonuclear granulocytes. Secondly, both the cutis and the muscle can be affected. In many cases there is a disproportion of the degree of local and systemic symptoms. Depending on the infectious agents there are two main types: type I is a polymicrobial infection and type II is a more invasive, serious, and fulminant monomicrobial infection mostly caused by group A Streptococcus pyogenes.Invasive, severe forms of streptococcal infections seem to occur more often in recent years. Multimodal and interdisciplinary therapy should be based on radical surgical débridement, systemic antibiotic therapy as well as enhanced intensive care therapy, which is sometimes combined with immunoglobulins (in streptococcal or staphylococcal infections) or hyperbaric oxygen therapy (HBOT, in clostridial infections). For wound care of extensive soft tissue defects vacuum-assisted closure has shown its benefit.

Pathogenic role of macrophages in intradermal infection of methicillin-resistant Staphylococcus aureus in thermally injured mice

Intradermal infection of methicillin-resistant Staphylococcus aureus (MRSA) in burned mice was pathogenically analyzed. An abscess was formed in normal mice intradermally infected with 10(8) CFU/mouse of MRSA, and all of these mice survived after the infection; however, abscess formation was not demonstrated to occur in burned mice similarly exposed to the pathogen, and all of these mice died within 5 days of infection. In burned mice, MRSA infected at the burn site intradermal tissues spread quickly throughout the whole body, while in normal mice, the pathogen remained localized at the infection site. Macrophages (Mφ) isolated from the infection site tissues of normal mice produced interleukin-12 (IL-12) but not IL-10 and were characterized as M1Mφ. These M1Mφ were not isolated from the infection site tissues of burned mice. When normal-mouse infection site tissue Mφ were adoptively transferred to burned mice at the MRSA infection site, an abscess formed, and the infection did not develop into sepsis. In contrast, an abscess did not form and sepsis developed in normal mice that were inoculated with burned-mouse infection site tissue Mφ. These Mφ produced IL-10 but not IL-12 and were characterized as M2Mφ. These results indicate that abscess formation is a major mechanism of host resistance against intradermal MRSA infection. M1Mφ in the tissues surrounding the infection site play a pivotal role in abscess formation; however, the abscess is not formed in burned mice where M2Mφ predominate. M2Mφ have been described as inhibitor cells for Mφ conversion from resident Mφ to M1Mφ.