The tools provided in the “Guideline for control of an healthcare-associated infection outbreak (WS/T 524-2016)” were used for epidemiological investigation . An outbreak emergency start-up procedure was implemented to detect and contain the HAI outbreak.
Emergency response criteria for a HAI outbreak were as follows:
Since the detection rate of a certain pathogenic microorganism in clinical specimens from a certain department has significantly increased, all the past cases within 7 calendar days of the department are reviewed from the date of specimen submission, and the emergency response is initiated if the following conditions are met:
① Within 7 calendar days, there were 2 cases or more of HAI or suspected cases of HAI caused by the same pathogenic microorganisms with highly similar antibiotic-susceptibility patterns;
② Within 3 calendar days, there were 3 cases or more of hospital-acquired cases (including colonization, HAI, and suspected HAI) caused by the same pathogenic microorganisms with highly similar antibiotic-susceptibility patterns;
With reference to the definition of Repeat Infection Timeframe (RIT) for HAI surveillance by the US National Healthcare Safety Network (NHSN) , we determined the following exclusion criteria:
① Cases that were judged to be contaminated by the pathogenic microorganisms or were taken outside the department;
② Patients whose infection had been cured;
③ Patients who had been hospitalized for a long time (excluding patients who had been hospitalized for more than 14 days after infection, but did not include new infections that have been identified), thereby avoiding frequent triggering of an emergency response by these patients.
The outbreak period was defined from December 28, 2018 to January 19, 2019. HAIs were defined according to the “HAI Diagnostic Criteria” issued by the Ministry of Health of the People’s Republic of China in 2001 .
Hand hygiene compliance observation
Since January 2016, the HAI management department and the nursing department of our hospital have jointly established a hand hygiene compliance monitoring team. After unified training, the team members used the WHO hand hygiene tools to measure monthly hand hygiene compliance in 92 wards of the hospital. To avoid observation bias, the observation unit was temporarily randomly assigned to each team member. During the outbreak, daily hand hygiene compliance supervision was performed by the NSICU head nurse using the same method.
A matched case-control study was performed to verify the suspicious factors leading to the HAI outbreak. The cases of HAI were defined as those who had stayed in the ICU for at least 48 h with CRAB infection or colonization, but it did not include cases of CRAB contamination and community infections.
Controls were patients who met the matching criteria. For each case patient, 2 control patients were randomly selected from the group of patients admitted to the NSICU during the same period who did not acquire CRAB.
Matching criteria were as follows:
① Patients with the same gender and in the same age group as the cases, and the age difference should be within 5 years;
② To avoid “time bias,” the selected controls should have sufficient length of hospitalization stay [17, 18]. Therefore, controls were patients who had been in the NSICU for an interval at least as long as that between the time of NSICU admission and isolation of CRAB for the case patient;
③ The Glasgow Coma Scale (GCS) of the controls should be in the same category as the cases, and the GCS difference should be within 2 scales. The GCS has a well-established profile for use in people who have sustained a traumatic brain injury, designating them into three severity categories; mild (GCS 13–15), moderate (9–12), and severe (3–8) categories .
Both clinical and environmental specimens were processed using standard techniques and reagents. Environmental sampling was performed after cleaning the entire unit. Environmental specimens were collected from suspected potential pollutants, including bed rails, door handles, curtains, computer keyboards and mice, ventilator control panel and sensor, air vents, mattresses, treatment carts, equipment tower surfaces, used rag and towel, staff hands, used medical textiles, sink inner surface, potable water, aerators, the outer surface of the faucets, and the inner surface of the proximal end of the water outlet. The entire exterior of aerators was sampled after dismantling. Pre-moistened cotton swabs were used to sample environmental specimens. The swabs were immediately inoculated onto sheep blood agar plates and incubated at 37 °C for 2 to 4 days.
The standard paper diffusion method and Vitek-2 (BioMerieux, France) automatic instrument detection was used to detect the sensitivity of AB to 21 commonly used antibiotics, including imipenem, meropenem, doripenem, ticarcillin, ampicillin/sulbactam, ceftriaxone, cefotaxime, cefepime, cefotetan, cefuroxime, cefoperazone/sulbactam, piperacillin/sulbactam, gentamicin, tobramycin, ciprofloxacin, amikacin, tetracycline, tigecycline, minocycline, amoxicillin/clavulanic acid, and aztreonam. Molecular typing was performed by the CHEF-Mapper PFGE system, and PFGE pattern clustering analysis was conducted by using BioNumerics Version 6.64. The PFGE classification was judged according to the discriminant proposed by Tenover et al. . Differences of more than 3 bands were considered to be of different types.
Infection control interventions
Intensive infection control measures were implemented according to the guideline (WS/T 524–2016) during the early outbreak (January 8–12, 2019). They included the following: (1) Strengthening measures to improve hand hygiene compliance were implemented. Healthcare workers’ (HCWs) hand hygiene compliance was checked twice daily, and violators were financially penalized. (2) Isolation was strictly enforced. Colonized/infected patients were separated into concentrated areas. (3) Fluorescent labeling was used to control the daily cleaning and disinfection effect of the ICU environment surface. (4) Aerosolized hydrogen peroxide was used to carry out terminal disinfection of individual wards in turn. (5) Unnecessary transfer of patients from other units or surrounding hospitals was stopped. (6) Contact precautions were practiced for all patients. (7) Medical staff and cleaning staff were retrained for an emergency response to the HAI outbreak.
From January 13, 2019, the use of all faucet aerators in the NSICU was prohibited. To avoid the infection risk of water-borne bacterial contamination due to splashing after the outbreak, all aerators were immersed once a week with chlorine disinfectant.
Statistical analysis of the data was performed using SPSS 23.0 software. A conditional logistic regression model for matched case-control groups was used to identify the factors associated with CRAB colonization and infection. All tests were 2-sided with an level of 0.05.