Background
Nosocomial infection (NI) which also called “hospital-acquired or health care-associated infection” is a serious public health issue affecting hundreds of millions of people every year worldwide [
1]
. NI is defined as an infection occurring in a patient admitted to the health-care settings for more than 48 but without any evidence that the infection was present or incubating at the time of admission [
1‐
3]
. In the hospitals or other health care facilities, NI is a leading cause of increased morbidity, mortality and financial burden [
1‐
7]
. The incidence of NI as most studies reporting data ranged from 3.6 to 12% in high-income countries [
8‐
10] and 5.7 to 19.1% in low- and middle-income coutries [
8,
11]
. Predisposing factors, i.e., the invasive procedures [
12‐
15], long hospital stay [
16], excessive antibiotics usage [
9] and the existence of severe illness [
17] lead to NI rate in patients admitted to the intensive care unit (ICU) several fold higher than that in the general hospital population [
18‐
21]
. Now, NI is more concerned as the focus of safety and quality improvements efforts in many hospitals. The study was designed to investigate the epidemiology, risk factors and outcome of NI in a Respiratory ICU (RICU) at the largest teaching hospital in Northwest China.
Methods
Study population
This study was conducted in RICU of the First Affiliated Hospital of Xi’an Jiaotong University, which is the largest hospital in Northwest China. It is a 2541-bed teaching hospital with a 16-bed RICU and about 3 millions outpatients annually. The nurse-to-patient ratio in RICU is about 1: 2–3 per shift. A total of 1347 patients admitted to the RICU for more than 48 h were included in the study from January 2013 to December 2015. NI was defined as an infection developed after 48 h of RICU admission and diagnosed according to the the American Center for Disease Control and Prevention (CDC) criteria [
22]
. In the study, the infection on a different site and with different pathogens from the primary infection that occurred at least 48 h after admission to the RICU was also classified as NI.
Data collection
The patients were followed until discharge from RICU or death, and the information on each patient was recorded on the standard surveillance paper chart. All patients with suspected infection underwent liver and renal function test, whole blood count、urine、fecal and coagulation profile examinations, chest radiography, blood、tracheal aspirate and other body fluids cultures as clinically indicated. Demographic information, i.e., the gender, age, admission and discharge dates, temperature, admission diagnosis, comorbidity, device use and the period of application, laboratory tests, chest radiographs, the isolated pathogens and susceptibility testing to antimicrobial agents, infection sites, drug usage were collected.
The assessment of ASIS
The disease severity was assessed by the Average Severity of Illness Score (ASIS), which was from the Standard for Nosocomial Infection Surveillance of China and established by China Ministry of Health. The criteria of ASIS was as follows: ASIS-A: The patients should be required only routine monitor without intensive care and treatment, and they usually discharged from ICU within 48 h; ASIS-B: The patients, such as the cases admitted to ICU to exclude myocarditis or myocardial infarction, were in stable condition and just required preventive monitor without intensive care and treatment; ASIS-C: The patients, such as those with chronic renal failure, were in stable condition and required intensive care; ASIS-D: The patients in unstable condition but without coma, shock and Disseminated Intravascular Coagulation (DIC), should be performed intensive care and treatment. The treatment should be regularly evaluated and adjusted; ASIS-E: The patients with unstable condition were in coma or shock. The cardio-pulmonary resuscitation, intensive care and treatment should be performed. The intensive care and treatment should be regularly evaluated and adjusted.
According to the Standard for Nosocomial Infection Surveillance of China, the gender, age, admission diagnosis, disease severity, comorbidity, immunosuppressive therapy and invasive procedures were investigated as the potential risk factors for NI in the study.
Research indexes and definitions
The prevalence of nosocomial infection rate was calculated by dividing the total number of nosocomial infections by the total number of patients (× 100). The device-associated nosocomial infection rate was calculated by dividing the total number of device-associated infection by the total days of device application (× 1000). The device utilization (DU) ratios was calculated by dividing the days of device application by the total patient days.
Statistical analysis
Statistical analyses were performed using SPSS 13.0 (serial number 5026743; SPSS Inc., Chicago, IL, USA). Descriptive frequencies were expressed using mean (standard deviation). Chi-square tests were used to compare the rates. For evaluating risk factors of NI, univariate analysis and multivariable logistic regression analysis were used to derive crude OR and adjusted OR, respectively. A p-value < 0.05 was considered statistically significant.
Discussion
NI causes increased morbidity, mortality and financial burden at the hospital setting [
1‐
7,
23]
. The infection surveillance and risk factors analysis are important prerequisites for the prevention and treatment of NI. At present, abundant literatures focus on the healthcare-associated infection [
4,
6,
9‐
11,
17], infection in ICU [
16,
18‐
21,
23] and device-associated infection [
12‐
15] have been reported. However, few studies on the topic of infection in RICU have been published. Thus, we conducted this prospective surveillance during 2013 and 2015 to determine the epidemiology and risk factors for NI in RICU at the First Affiliated Hospital of Xi’an Jiaotong University, China. But it was a single cente study and from the largest hospital in Northwest China. The selective bias of the study may affect the generalization of the results.
In our study, there was no significant change in the incidence rate of NI over the 3 years. The overall prevalence of NI in RICU was 7.57%, which was lower than the published rates in European survey (8%) [
24] and in India (33.5%) [
25]. The mean length of stay was 8.54 days, which was lower than that reported in Italy [
26]
. In our RICU, COPD was the common underlying diseases, which is in agreement with the published study [
26]
. Similar to previous reports from other countries,
24, 25 the most frequently isolated pathogens were
Staphylococcus aureus, Klebsiella pneumoniae and
Pseudomonas aeruginosa. The common distribution of RICU infections were lower respiratory tract, urinary tract and bloodstream, this is similar to the reports for ICU infection in China [
15], European [
9,
16] and Malaysian [
27]
.
In the present study, the device-associated infection accounted for the most of RICU-acquired infections (85.3%). The device utilization ratios (0.14–0.42) were lower than the published rates in Europe, Malaysian and surveys from 61 countries (0.52–0.95) [
12,
14,
27‐
29]
. The VAP rate in our study was significantly lower than that in Greece [
14], Malaysian [
27]and surveys from 61 countries [
28,
29] where the rates varied from 13.6 to 20 per 1000 days. The CAUTI rate in our study was lower than that in Malaysian (15.6 per 1000 days) [
27], but higher than the published rates (4.2–6.3 per 1000 days) [
14,
28,
29]
. The CABSI rate in the present study was lower than that in Greece (11.8 per 1000 days) [
14], but higher than that in Malaysian (3.0 per 1000 days) [
27]
.
Previous studies [
11,
14,
16,
17,
25,
30] indicated that surgery, device utilization, antimicrobial use and length of stay were the risk factors for NI. In our study, the incidence of RICU infection in patients with stay (≥ 10 days), ASIS-C˴ D˴ E, lung cancer, trauma, diabetes mellitus, immunosuppressive therapy, tracheotomy, device utilization was significant higher than that in the control patients (
P < 0.05). But only ASIS-D˴ E, stay ≥10 days, immunosuppressive therapy and ventilator utilization are independent risk factors for RICU infection (
P < 0.05). The incidence of death in patients with NI was 2.32 times to those without NI.
Conclusions
In conclusion, a relatively low and stable rate of NI was observed in our RICU through year 2013–2015. ASIS-D˴ E, stay ≥10 days, immunosuppressive therapy and ventilator use are independent risk factors for developing infection in our RICU. High mortality rates in patients with infection suggest that infection control activities in RICU must be constantly maintained in order to reduce the rate.
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