Patient demographics During the 10-year study period, a total of 210 patients with PDNI were identified, and thirty six cases were excluded from the study. Ultimately, a cohort of 174 eligible cases was enrolled into this study. Of them, 117 were males (67.2%) and 57 were females (32.8%), with a male-to-female ratio of 2.05/1. The mean age of the patients was 51.3 ± 15.6 years (range, 15–88 years), with the age distribution of patients curve peaked in the fifth decade of life (42/174, 24.1%), followed by sixth decade (39/174, 22.4%). The age and sex distribution is shown in Fig.1. Among the 174 patients, 62 (35.6%) were working persons, 112 (64.4%) were non-working (students, unemployed persons, farmers, retired people). Throughout the study period, the number of inpatients treated was steady during the first four years, however, it showed an upward trend in the number of presented cases since 2013, while there were four cases of PDNI in 2009, it increased to 35 cases in 2018, with peak prevalence in 2017 (43 cases). The chronological distribution of the PDNI patients is showed in Fig. 2. The number of PDNI inpatients was highest in December (21 patients) and lowest in July (9 patients) (Fig. 3). The most common season for PDNI was winter (31.03%, 54/174), followed by fall (28.74%, 50/174), summer (20.69%, 36/174), and spring (19.54%, 34/174). PDNI was found year-round, however, winter seemed much more common. Table 1 shows the baseline demographics of all the patients.
Predisposing factor There were 114 patients (65.5%) who had underlying systemic diseases; 81 were men, and 33 were women, with a mean age of 52.9±14.35 years. In this patient group, the most common predisposing factor was type-2 DM in 70 patients (40.2%), followed by hypoalbumin in 62 patients (35.6%) and anemia in 56 patients (Table 2). Ninety five patients (54.6%) were smokers, and 58 patients (33.3%) were alcoholics. There was no case of known intravenous drug abuse, or known primary or acquired immunodeficiency.
Clinical features Posterior neck abscess formation was noted in 170 patients (97.7%) and cervical necrotizing fasciitis in only four patients (2.3%). Each one of representative case was shown in Fig. 4 and Fig. 5.
The mean time from symptom onset to the demand for health services was 11.0 ± 6.9 days (range, 1–30 days). The most common presenting symptoms on admission were neck pain (158 cases, 90.8%), followed by local neck swelling and had a progressive increase in size in few last days, and neck erythema, documented in 148 (85.1%) and 134 (77%) patients, respectively.
The mean body temperature at presentation was 37.2±0.79°C (range, 36.5–39.6°C). At admission, physical examination revealed that 7 patients (4.0%) had signs of bacteremia or septic shock at the time of diagnosis, and those collected blood cultures. A summary of the clinical features of the patient cohort are presented in Table 3.
Diagnostic procedure
Laboratory findings Regarding the laboratory test findings, the mean±SD values at the time of admission were: WBC count = 13.18 ± 8.08 ×109/L (range, 1.87–39.95 ×109/L) and neutrophils count = 10.88 ± 7.71 ×109/L (range 1.14–29.29 ×109/L) in all the 174 cases with available data, respectively. In addition, leukocytosis (WBC >11.0 ×109/L) was detected in 54 patients (31.0%), and leukopenia (WBC <4.0 ×109/L) in six patients (3.4%). Twenty four patients (13.8%) had a WBC count of more than 20.0×109/L. Hemoglobin = 119.3 ± 23.66 g/L (range, 50–179 g/L) in all the 174 cases with available data, with a lower than 120 g/L in male or 110 g/L in female was found in 56 patients (32.2%). Serum albumin = 29.70 ± 7.12 g/L (range, 12.7–44.2 g/L) in 166 of 174 cases with available data, with hypoalbumin (< 30g/L) was found in 62 patients (37.3%). Blood glucose = 9.79 ± 5.61 mmol/L (range, 3.66–28.38 mmol/L) in 170 of 174 cases with available data, with an elevation of blood glucose (>11.1 mmol/L) in 40 patients (23.5%). Glycated hemoglobin= 10.06 ± 2.72 % (range, 5.2–14.5 %) in 76 of 174 patients with available data, with poor control of blood glucose was found in 33 patients (> 7%). CRP = 155.89 ± 116.10 mg/L (range, 2.7–525.0 mg/L) in 146 of 174 cases with available data, with 68 cases (46.6%) had the elevation of CRP level (>3.5 mg/L).
Blood cultures were routinely checked for patients with signs of sepsis, resulting positive cultures in 7 patients, with the most prevalent occurrence of Klebsiella pneumoniae (2 cases). Laboratory data at admission was presented in Table 4.
Bacteriology The results of bacterial cultures were available for 150 of the 174 cases who underwent surgical treatment or wound swabs (86.2%). Bacteriological samples were missing in 24 patients. There were 111 of those patients (74%) had identifiable bacterial growths, and the remaining 39 cultures showed no bacterial growth (26%). The most commonly isolated organisms of the positive culture were Staphylococcus aureus [n=45, 30%; including 4 methicillin-resistant S. aureus (MRSA)], followed by Escherichia coli (n=15, 10%) and Klebsiella pneumoniae (n=11, 7.3%). Polymicrobial culture was detected in 13 patients (8.7%, 2–3 species). The microbiology findings are summarized in Table 5.
Imaging findings In the current study, only a few patients underwent imaging: 21 cases (12.1%) had ultrasound scanning, 4 cases (2.3%) underwent neck soft tissue x-ray, and 6 patients (3.4%) underwent CT scan. None of the patient underwent magnetic resonance imaging or other imaging examination.
Treatment protocol, complication and outcome Thirty four out of 174 patients (76.5%) had been previously treated before admission, 16 patients (9.2%) underwent surgical intervention combined with antibiotic therapy in regional hospital, and 18 patients (10.3%) were already treated with antibiotics alone, orally or intravenously, in regional hospital, clinics or by themselves. Notably, thirteen patients (7.5%) used traditional Chinese medicine topically themselves prior to their first visit to our institution.
After admission, all the patients initially received broad-spectrum intravenous antimicrobial therapy empirically at their presentation, in order to cover the majority of aerobic, gram-negative and gram-positive organisms involved in PDNIs. The antimicrobial agents and their doses were then adjusted according to microbiological bacterial culture and clinical response.
The most common treatment regimens of empirical antibiotics were vancomycin (n= 38, 21.3%), followed by cefepime (n= 32, 18.4%) and meropenem (n= 31, 17.8%), cefuroxime (n= 26, 14.9%), ceftriaxone (n= 19, 10.9%) and ornidazole (n= 14, 8.0%). Other antibiotics used in this study group were as follows: levofloxacin (n= 8, 4.6%), cefoperazone tazobactam (n= 6, 3.4%), tigecycline (n= 5, 2.9%), imipenem (n= 4, 2.3%), mezlocillin sodium and sulbactam sodium (n= 4, 2.3%), teicoplanin (n= 3, 1.7%), moxifloxacin (n= 3, 1.7%), penicillin sodium (n= 2, 1.1%), ceftezole (n= 1, 0.6%), flucloxacillin sodium (n= 1, 0.6%), sulfoxil sodium (n= 1, 0.6%), cephalosporin (n= 1, 0.6%) and doxycycline (n= 1, 0.6%).
In this study, all the patients underwent aggressive surgery, including debridement of necrotic tissue, primary suture and drainage, and secondary skin grafting. Most of the patients (146/174, 83.9%) received the first surgery within 24 h. The mean time intervals from hospital admission until surgery was 1 day (range, 0–5 days). Seventy six patients (43.7%) were subjected to a series of surgeries (2-4 operations).
In addition, supportive medical treatments was also initiated when required, which included fluid therapy, analgesics, nutritional support, blood transfusion, control of blood glucose, and antipyretics. When patients with decompensated systemic diseases were involved, appropriate specialists, mostly endocrinologist, cardiologist or internal medicine specialists, were consulted regarding the therapy.
Life-threatening complications were developed in seven cases (4.0%), including bacteremia in four cases and septic shock in three cases. All the patients were discharged in stable condition, with the mean length of stay was 28.7±12.95 days (range, 12-63 days). None of our patient died of PDNI or its complication. Those patients with underlying systemic diseases (31.4 ± 12.35 days) or complications (41.0 ± 12.5 days) tended to have a longer hospital stay. The mean cost of admission per patient was 47 644 RMB (range, 5 848 - 303 579 RMB). Signs of cellulitis in two patients and abscess in one patient were found and they were hospitalized again for management.