Effects of infection control measures on acquisition of five antimicrobial drug-resistant microorganisms in a tetanus intensive care unit in Vietnam

Abstract

Purpose: To quantify the effects of barrier precautions and antibiotic mixing on prevalence and acquisition of five drug-resistant microorganisms within a single tetanus intensive care unit at a tertiary referral hospital in Ho Chi Minh City, Vietnam.

Methods: All patients admitted within the study period were included. After a 1-year baseline period, barrier precautions were implemented and the single empirical treatment ceftazidime was changed to mixing (per consecutive patient) of three different regimens (ceftazidime, ciprofloxacin, piperacillin-tazobactam). Markov chain modeling and genotyping were used to determine the effects of interventions on prevalence levels and the relative importance of cross-transmission and antibiotic-associated selection.

Results: A total of 190 patients were included in year 1 (2,708 patient days, 17,260 cultures) and 167 patients in year 2 (3,384 patient days, 20,580 cultures). In year 1, average daily prevalence rates for methicillin-resistant Staphylococcus aureus (MRSA), extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae (excluding Klebsiella pneumoniae), Pseudomonas aeruginosa, gentamicin-resistant K. pneumoniae, and amikacin-resistant Acinetobacter species were 34.0, 61.3, 53.4, 65.7 and 57.1 %. After intervention, ceftazidime usage decreased by 53 %; the use of piperacillin-tazobactam and ciprofloxacin increased 7.2-fold and 4.5-fold, respectively. Adherence to hand hygiene after patient contact was 54 %. These measures were associated with a reduction of MRSA prevalence by 69.8 % (to 10.3 %), mainly because of less cross-transmission (88 % reduction), and of ESBL-producing Enterobacteriaceae prevalence by 10.3 % (non-significantly). In contrast, prevalence levels of the other three pathogens remained unaffected.

Conclusion: The combination of simple infection control measures and antibiotic mixing was highly effective in reducing the prevalence of MRSA, but not of Gram-negative microorganisms.

Fig. 1

Estimated prevalence of Pseudomonas aeruginosa (a), gentamicin-resistant Klebsiella pneumoniae (b), amikacin-resistant Acinetobacter spp. (c), methicillin-resistant Staphylococcus aureus (d), extended spectrum beta-lactamase-producing Enterobacteriaceae (excl. K. pneumoniae) (e) on tetanus intensive care unit during year 1 (May 2004–April 2005) and year 2 (May 2005–April 2006). Red indicates the number of patients colonized at a given time point, green the number of patients uncolonized, and blue the number of patients with unknown colonization status, i.e., patient days between the last negative culture result and the first positive culture result, or patient days between the last negative result and discharge

Fig. 2

Contour plots of the likelihood of the acquisition parameters α (endogenous acquisition, horizontal axis) and β (exogenous acquisition, vertical axis) for Pseudomonas aeruginosa, gentamicin-resistant Klebsiella pneumoniae, amikacin-resistant Acinetobacter spp., methicillin-resistant Staphylococcus aureus (MRSA), extended spectrum beta-lactamase-producing Enterobacteriaceae (excl. K. pneumoniae) (ESBL-producing Enterobacteriaceae) in year 1 and year 2. The black dot represents the maximum likelihood estimate (MLE), the shaded area represents the corresponding 95 % confidence interval (CI). The line represents the parameters for which the endogenous route and the exogenous route are equally important. For example, the MLE of exogenous acquisition parameter β of MRSA was 0.117 (95 % CI 0.079; 0.162) in year 1 and 0.015 (0.0; 0.055) in year 2, indicating that the probability of exogenous acquisition of MRSA per unit of time for a given prevalence of MRSA on the ward was 8 (0.117/0.015) times lower in year 2 compared to year 1. In contrast, the MLEs of endogenous acquisition parameter α were both 0.005 (95 % CI 0.002; 0.012 and 0.002; 0.009) in year 1 and year 2, indicating that the daily probability of endogenous acquisition of MRSA remained 0.5 % throughout the entire study period

Fig. 3

Pulse field gel electrophoreses analysis of all first methicillin-resistant Staphylococcus aureus (MRSA) strains, isolated from patients admitted to the tetanus ICU during the entire study period (May 2004–April 2006). Band patterns were generated by restriction enzyme digestion of total bacterial DNA. Each row depicts the band pattern of a single isolate and the date of sample collection (first column), date of admission (second column), and date of discharge (third column) of the patient the isolate was cultured from. Identical band patterns indicate clonality as can be expected after exogenous transmission of MRSA