Introduction

Necrotizing soft tissue infection (NSTI) is a severe, rapidly progressive disease that is characterized by the infection of subcutaneous tissue and fascia, resulting in extensive fascial necrosis [1]. The gold standard management for NSTI is rapid debridement and broad-spectrum antibiotics [2]. Even under rapid and timely management, the risk of mortality and morbidity, such as amputation and multiorgan dysfunction, remains high [3,4,5]. NSTI caused by Vibrio vulnificus is a life-threatening condition with rapid progression and high mortality. It usually occurs through the injuries sustained when handling seafood, wound exposure to seawater, and ingestion of contaminated under-cooked seafood. Immunocompromised patients are also at higher risk of developing this disease [6,7,8].

Mortality from NSTI caused by gram-negative pathogens has been reported to be higher than caused by other pathogens in warm costal area [9]; however, it remains unclear whether mortality from V. vulnificus NSTI is higher than mortality from non-Vibrio NSTI. Only a few studies have compared mortality between V. vulnificus NSTI and non-Vibrio NSTI; one showed that the clinical features of V. vulnificus infection were more rapidly progressive and fulminant than those of the methicillin-resistant Staphylococcus aureus (MRSA) or MSSA infection [10], whereas another showed that the laboratory risk indicator for necrotizing fasciitis (LRINEC) score was inaccurate in necrotizing fasciitis caused by V. vulnificus. [11]. The aim of the present study was to examine the differences in in-hospital mortality between patients with V. vulnificus NSTI and those with non-Vibrio NSTI, adjusting for comorbidities.

Material and methods

Patient selection

Under the approval of institutional review board, a retrospective cohort study was conducted. The medical records of patients who met the inclusion criteria of surgically proven NSTI and who received management between 2015 and 2020 in two tertiary hospitals were reviewed. Among the patients with NSTI, we selected V. vulnificus group and non-Vibrio group with 1:2 matching: For each patient in the V. vulnificus group, we identified two non-Vibrio patients of the same sex who were admitted to the same hospital in the same year and whose ages were within 5 years of the age of the V. vulnificus patient. We defined V. vulnificus NSTI group as blood culture or surgical wound culture yields V. vulnificus, or both yield V. vulnificus.

Data collection and analysis

Age, sex, vital signs in the emergency department (ED), hospital stay, the presence of comorbidities, and blood biochemistry profile were analyzed. After data collection was completed, random chart reviews were performed to ensure accuracy. We used hospital identifiers for matching to cancel out site-specific effects such as physician practice patterns and treatment outcomes. We performed multiple imputation for missing data on systolic blood pressure, body temperature, heart rate, and biochemistry analysis of blood. We replaced each missing value with a set of substituted plausible values by generating multiple datasets using the multivariate imputation by chained equations method. The following covariates were used to create these 10 complete datasets: V. vulnificus NSTI, age, sex, comorbidity, seawater or seafood contact, serum lactate, LRINEC (laboratory risk indicator for necrotizing fasciitis) sore, in-hospital death, and 30-day in-hospital death, with the assumption that data were missing at random. Estimates from these imputed datasets were combined using Rubin’s rule to obtain combined imputation estimates and standard errors. Then, using multivariable logistic regression analysis fitted with generalized estimating equations to account for the 1:2 matched-pair clustering, we examined the factors associated with all-cause in-hospital mortality.

Outcomes

The primary outcome of this study was all-cause in-hospital mortality. The secondary outcomes were 30-day in-hospital mortality and length of stay.

Statistical analysis

All data were analyzed using the Statistical Package for the Social Sciences software, version 20.0 (IBM Corp., Armonk, NY, USA). The chi-square test was used to compare proportions between groups. The two-sample t test was used to compare average values, and the Mann–Whitney test was used to compare the median values between groups. Using multivariable logistic regression analysis fitted with generalized estimating equations to account for the 1:2 matched-pair clustering, we examined the factors associated with all-cause in-hospital mortality. Multiple linear regression analysis fitted with generalized estimating equations.

Results

A total of 135 patients were included, 45 in V. vulnificus NSTI group and 90 in non-Vibrio group. The mean age was 69.3 years (standard deviation [SD] = 12.7), and 66.4% of the patients were male. Table 1 shows the characteristics of patients with V. vulnificus NSTI and non-Vibrio NSTI after 1:2 matching. The V. vulnificus NSTI group tended to have hypotension, bacteremia, history of seawater or seafood contact, comorbidity with liver disease, and higher serum lactate. All-cause in-hospital mortality was 13.3% in the V. vulnificus NSTI, whereas it was 7.8% in the non-Vibrio NSTI (Table 2.). All-cause 30-day was also higher in the V. vulnificus NSTI than in the non-Vibrio group. Length of hospital stay was longer in the V. vulnificus NSTI than in the non-Vibrio group. Table 3 shows the results of the multivariable logistic regression analysis with generalized estimating equations after multiple imputation for all-cause in-hospital mortality. V. vulnificus NSTI was significantly associated with higher mortality compared with non-Vibrio group (adjusted odds ratio = 1.52; 95% confidence interval 1.36–1.70; p < 0.01). Higher mortality was significantly associated with higher serum lactate, higher LRINEC score, and with liver disease.

Table 1 Clinical characteristics between V. vulnificus and non-Vibrio groups
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Table 2 Outcomes of patients with V. vulnificus and non-Vibrio after 1:2 matching
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Table 3 Multivariable logistic regression analysis with generalized estimating equations accounting for clustering within matched pairs for all-cause in-hospital mortality
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Discussion

Vibrio vulnificus is a gram-negative marine bacterium that is usually present in warm coastal waters. The main clinical manifestations of V. vulnificus infections in humans are gastrointestinal illnesses, primary septicemia, and wound infections. The clinical course can progress rapidly by releasing hemolysins and proteases and result in hemorrhagic bullae and severe skin necrosis [10, 12, 13]. The routes of necrotizing soft tissue infection caused by V. vulnificus include wound infections while handling seafood, exposure of a preexisting wound to seawater, and ingestion of contaminated under-cooked seafood [12,13,14].

Using two tertiary hospital database in Southern Taiwan, our study showed that mortality was higher in patients with V. vulnificus NSTI than those in non-Vibrio group. In our study, in-hospital mortality among patients with V. vulnificus NSTI was 13.3%. Previous studies have reported vulnificus NSTI mortality around 10–13% [9, 15], which is comparable to our results. Mortality from NSTI caused by gram-negative or monomicrobial pathogen has been reported to be higher than caused by other pathogens. Namany et al. [16] found that monomicrobial disease group had a significantly higher 90-day mortality rate in addition to higher rates of in-hospital mortality, ICU admission, and vasopressor use than the polymicrobial disease group. Huang et al. [17] revealed that NSTI caused by monomicrobial Aeromonas spp. revealed high mortality rates, even through aggressive surgical debridement and antibacterial therapies. They all raised concern for increasing risk of monomicrobial infection and gram-negative pathogen. As comparison, the non-Vibrio group are including gram-positive, negative, and culture no growth patients, and possibly monomicrobial or polymicrobial. Mainly pathogens included Aeromonas spp., Pseudomonas, Escherichia coli, Klebsiella pneumoniae, Staphylococcus, and Streptococcus spp. (There are 39 monomicrobial gram-positive, 10 monomicrobial negative, 15 polymicrobial, and 26 culture no growth in non-Vibrio group in our data.)

In V. vulnificus NSTI, there are 17 patients with positive blood and wound culture (37.8%), 12 patients with positive blood culture (26.7%), and 16 patients with positive wound culture (35.5%). In non-Vibrio group, there are 19 patients with bacteremia (21.1%). V. vulnificus group had higher incidence of bacteremia than non-Vibrio group (64.4% vs 21.1%). Tsai et.al conducted a study about NSTI patients with V. vulnificus and methicillin-resistant Staphylococcus aureus (MRSA). The incidence of bacteremia was 65% vs 18.75%; V. vulnificus group was also higher than MRSA group [9]. Immune-compromised and chronic liver disease (chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma) patients with V. vulnificus are more likely to develop blood stream infections [6, 18, 19]. In our study, the incidence of chronic liver disease was also higher in V. vulnificus group. Vibrio vulnificus can produce Vibrio vulnificus hemolysin/cytolysin (VVH), multifunctional autoprocessing RTX toxin, Vibrio vulnificus serine protease (VvsA), and Vibrio vulnificus protease (VVP). Both VVH and RTX toxin contribute to bacterial invasion to the blood stream and play a role in the development of hypotensive septic shock. The RTX toxin may promote the colonization at the primary infection site and cause severe tissue damage by releasing degrading cytotoxins to induce the inflammatory responses, that Vibrio vulnificus can then spread to the blood stream to result in systemic manifestations. Both VVP and VvsA are produced in the interstitial tissues of limbs and cause serious collagenolytic, hemorrhagic, or edematous skin damage in the extremities [9, 20,21,22,23]. The specific toxin of V. vulnificus may explain a relatively higher rate of blood steam infection than other pathogens. However, the comparison of Vibrio vulnificus bacteremia between NSTI and food-borne infection settings needs further studies.

Studies have shown conflicting results on the difference in mortality between patients with NSTI in subgroups. One study had shown higher mortality for NSTI patients with Aeromonas species than for those with V. vulnificus [24]. One study had shown no significant differences of mortality between NSTI patients with V. vulnificus and Klebsiella pneumoniae [25]. Another recent study has shown no significant differences of mortality between NSTI patients with V. vulnificus and MRSA [9]. But few studies have focused on V. vulnificus versus non-Vibrio NSTI. In the present study, we clearly demonstrated that mortality was higher in patients with V. vulnificus than in patients with non-Vibrio NSTI. Besides, longer hospital stay may lead to higher hospitalization cost in V. vulnificus NSTI.

Our study showed that patients with hepatic dysfunction had significant associations with V. vulnificus infections and mortality. There were studies considered liver cirrhosis as risk factor with increased mortality among NSTI patients [9, 26,27,28,29]. Previous study had demonstrated that hyperlactatemia is significantly associated with in-hospital mortality in NSTI patients, even after adjusting for acidosis [30, 31]. The result was similar in the present study, even in V. vulnificus infection. Because NSTI and its rapidly progressive infection remain associated with high mortality, the LRINEC score, developed by Wong et al. [32] based on readily available laboratory markers, has been consistently evaluated for its efficacy in various studies. One study has been reported to be inaccurate in necrotizing fasciitis caused by V. vulnificus [11]. However, we found the higher LRINEC score may not help early diagnosis with V. vulnificus NSTI but display a significant role with prognosis, associated with higher mortality in V. vulnificus NSTI patients.

This study still has some limitations. First, this study lacks external validation. The validity of the result still requires other studies to confirm. Second, the retrospective design of this study had its inherent limitation in data collection, such as unverified comorbidities. Third, the sample size is relatively small due to the rarity of NSTI. Fourth, the degree of liver disease in each group is not clearly stated.

Conclusions

In summary, adjusted in-hospital mortality was significantly higher for patients with V. vulnificus NSTI than for those with non-Vibrio NSTI in this matched-pair cohort study. Preventing V. vulnificus infection is essential. The validity of the result still needs to be confirmed by further studies.