Eight strains of S. flexneri 2a were isolated from fresh fecal specimens of 12 patients (average age 48.9±18.9 years old; youngest patient was seventeen and the oldest one was seventy-four years old) with diarrhea from the same ward of Xiaoshan Mental Healthcare Center in Hangzhou, China. The Mental Healthcare Centre is a fully enclosed medical and rehabilitation institution, which is divided into male ward, female ward and intensive care area. The outbreak occurred in the male ward with twenty-five patients; twelve patients had different degrees of diarrhea accompanied by high temperature (>38 °C) with blood-free mucus feces. Finally, a total of eight Shigella strains were isolated from twelve samples and the serotype of all isolates were flexneri 2a.
The investigation showed that no doctors, nurses or nursing workers were infected with Shigella. Interestingly, S. flexneri 2a was detected in stool sample of a canteen staff worker (his job was to distribute food to patients in the male wards). The staff member suffered from diarrhea and abdominal pain. Those symptoms accrued before the outbreak in patients, which suggested the worker was likely to be a source of infection. Moreover, the serotype, drug sensitivity, resistance and virulence genes of the strain were the same as that in the Shigella presented in the outbreak.
Furthermore, in March 2013, we isolated the S. flexneri 2a from feces of two patients who have been infected with Shigella. In February 2014, one S. flexneri 2a was isolated from patient with initial infection. Then we confirmed that these isolates belong to the same clone as the outbreak strains. After that, we continued the monitoring for three years, except for four patients who had been discharged from the hospital. The investigation ended in December 2016. This phenomenon suggests that patients infected with Shigella do not have long-term immunity; it may turn into a latent infection under the intervention of antibiotics, and relapse when the body's immune system decreases.
All 8 S. flexneri 2a isolates were resistant to ampicillin, trimethoprim/sulfamethoxazole, tetracycline, cefotaxime, ceftazidime, cefepime, ciprofloxacin, but were sensitive to piperacillin/tazobactam, imipenem, and the MIC of azithromycin was 2 μg/mL (no interpretation standard) (Table 1). Moreover, all strains produced extended-spectrum β-lactamase (ESBL). In addition, the PCR and sequencing results showed that all outbreak isolates carried blaCTX-M-57, blaOXA-30, blaTEM-1 resistant genes and ia1, ipaH, setlB, sen and virA virulence genes. Meanwhile, the gyrA (Ser83Leu) and parC (Ser80Ile) amino acid mutations were discovered in quinolone resistance determining regions (QRDRs) (Table 2). Also, the PFGE results showed that all 9 S. flexneri 2a isolates (including the strain isolated from canteen staff) had the same band patterns, which indicated that they belong to the same clone (Figure 1).
During the outbreak of the epidemic, the hospital took emergency preventive and control measures, including patient isolation, environmental disinfection, propaganda and education on hand hygiene, sanitary management of food and water, improvement of ventilation conditions, medical observation of close contacts.
All patients infected with S. flexneri 2a were treated with antibiotics. At the initial stage of infection, 3 patients were treated with intravenous cefotaxime (3.0gV/BID), 3 patients with oral norfloxacin (0.2g/TID), 1 patient with oral sulfamethoxazole (2g/BID) and 1 with intravenous piperacillin/tazobactam (3.375g/Q8H). However, five patients failed to receive effective treatment. Because the S. flexneri 2a isolates produce ESBL and quinolone-resistance, we recommended piperacillin/tazobactam or azithromycin as the main treatment approach for those patients. Consequently, the antibiotics were substituted with intravenous piperacillin/tazobactam 3.375g/Q8H and intravenous cefoperazone/sulbactam 3.0g/BID. All the infected patients were cured and five consecutive cultures of Shigella revealed to be negative.