Surveillance of catheter-related infections: the supplementary role of the microbiology laboratory

Catheter-related infections pose an unrecognised threat to patient safety. The results of the study showed that laboratory surveillance plays an important role in establishing baseline data of CRIs in a setting with limited resources. The number of patient admissions or the number of in-patient days can effectively describe the hospital-wide prevalence of these infections, especially where the collection of catheter days is problematic, as previously showed by Rodríguez-Créixems and colleagues [18].

Comparing MC-CRBSI rates between surveillance networks are difficult, since the numerator (i.e. case definition of a CRI) and the denominators (i.e. 1 000 catheter days, in-patient days or admissions) applied, vary greatly. If one compare our MC-CRBSI rate (10.1 per 1 000 catheter days; 0.57 per 1 000 in-patient days or 3.7 per 1 000 admissions), regardless of the reporting denominator, to studies in Europe (2.1 per 1 000 catheter days) [19], Spain (2.5 per 1 000 admissions) [18], Israel (0.21 per 1 000 in-patient days) [22] and by the International Nosocomial Infection Control Consortium (4.8 per 1 000 catheter days) [23], our MC-CRBSI rate was higher.

Reasons argued to contribute to a higher CRI rate includes: i) a low nurse-to-patient ratio, ii) a lack of education, iii) nurse inexperience and iv) a lack of infection control legislation [4]. In South Africa, a survey of public medical and surgical unit nurses showed that the nurse-to-patient ratio ranged from 8.75 to 32 [17], whereas a national audit showed that there are 0.3 trained ICU nurses per ICU/high care bed [24]. Furthermore, only 25.6% (1 490/5 821) of ICU nurses were formally trained in critical care and 42.8% (1 961/4 578) had zero to five years of experience [24]. Draft legislation passed in 2008 by the South African National Department of Health, proposed one infection control practitioner per 200 beds [13]. A human resource capacity survey followed and found that no healthcare facility had the required number of infection control practitioners and that 45.8% (116/253) of the respondents were not formally employed; performed infection control activities part-time or out of personal interest and did not have additional support from an epidemiologist or a microbiologist [13].

Studies comparing the laboratory-based MC-CRBSI rates with the classical hospital-based CLABSI rates are scarce [18]. If one compares our laboratory-based MC-CRBSI rate to the BCA campaign’s CLABSI rate, one will note that the MC-CRBSI rate was higher in most of the wards. This seems odd at first, since hospital-based CLABSI surveillance tends to overestimate the actual CRI rate, whereas laboratory-based MC-CRBSI tends to underestimate the actual CRI rate [25]. However, an important contributing factor, which will explain the difference between the two rates, is the point at which the CRI incidence is measured. Laboratory-based MC-CRBSI rates are measured at the point of catheter removal, whereas hospital-based CLABSI rates are measured at the point of catheter insertion. Comparison of CLABSI rates with MC-CRBSI rates may in future be used as a measurement to evaluate the effectiveness of catheter maintenance practices against catheter insertion practices. The two wards with a higher CLABSI rate and a lower MC-CRBSI rate had a low number of catheter tips accompanied by BCs within 48 h (Table 1) and microbiological documentation, as such, is known to bias the true CRI rate [26].

Staphylococcus epidermidis was the most prevalent aetiological agent, followed by Acinetobacter baumannii complex. It can be argued that the criteria to include a single positive BC for common commensals can inflate the prevalence of S. epidermidis. However, the genetic relationship between the catheter tip and BC isolates of S. epidermidis isolates was confirmed with pulsed-field gel electrophoresis. A notable exception to the distribution of CRI pathogens in the study is the predominance of A. baumannii. Enterococci and Candida species are more predominant in the USA, whereas Pseudomonas aeruginosa and Escherichia coli are more predominant in Europe [27,28]. The high proportion of the MC-CRBSI episodes caused by Gram-negative bacilli is suggestive of a potential bias either at institutional level or on patient-level. A study by Bouza and colleagues showed that patients with a Gram-negative CRI were more likely to have an underlying gastro-intestinal condition and were previously exposed to antimicrobials, which were similar to the patients involved in the current study [29].

A shift in the predominance of CRI pathogens, from Gram-positive to Gram-negative bacteria, is widely reported, which suggests that central line insertion bundles are more effective in reducing Gram-positive CRI than Gram-negative CRI [18,22,30-32]. The high prevalence of S. epidermidis CRI therefore implies failure towards central line insertion bundle adherence. Urgent attention needs to be paid to the education and training of healthcare personnel involved in catheter insertion, not only to decrease the rate of MC-CRBSI, but to ensure patient safety.

Acinetobacter baumannii is listed by the Infectious Disease Society of America as one of the six top-priority dangerous microorganisms, which makes the predominance of this pathogen in the study a matter of concern. The hospital environment (i.e. bed rails, mattresses, medical equipment, colonised or infected patients and the hands of healthcare workers) is an ecological niche for A. baumannii and resistance to desiccation, disinfections and antimicrobials makes eradication of this pathogen difficult [33]. All A. baumannii isolates was defined XDR in the study, with isolates only being susceptible to colistin. Although empirical antibiotic therapy for Gram-negative CRIs is based on local epidemiology, caution should be exercised in recommending colistin monotherapy in the management of CRI patients. Colistin-resistance in A. baumannii, which is associated with the inappropriate use thereof, can emerge rapidly, due to chromosomal mutations [34]. Combination therapy of colistin and a carbapenem should rather be used to prevent the emergence of colistin-resistant A. baumannii [34]. Extensive environmental decontamination, such as daily chlorhexidine bathing and oral care of colonised or infected patients, as well the use of an oxidizing disinfectant (Virkon S; potassium peroxomonosulphate 50%, sodium alkyl benzene sulphonate 15% and sulphamic acid 5%), should be considered to control and prevent further spread of A. baumannii [35,36].

The study had a number of limitations. First, it is important to note that the definition applied is highly specific and that some cases of CRIs might have been missed. In future, criteria, such as the clinical improvement of the patient after line removal, which is suggestive of a CRI and other diagnostic methods, such as differential time to positivity, which might be more appropriate in oncology and haematological patient populations, should be included to obtain a more reliable CRI rate. Second, the Acute Physiological Assessment and Chronic Health Evaluation (APACHE) II severity of illness score could not be determined and no comment can be made on the appropriateness of antimicrobial chemotherapy, since the initial reason for therapy, dosage, the administration route and the duration of treatment were unknown. However, it is known that the majority of patients were exposed to two or more antimicrobial agents during hospitalisation, such as carbapenems and glycopeptides. This is worrying, due to the strong association between the over usage of antimicrobials and the selection of resistance in microorganisms. The device utilisation rate could not be calculated, since the number of in-patient days, for the wards where catheter days were collected, was unknown. Lastly, the study cannot be extrapolated to the entirety of South Africa, since a single institution is not representative of the country.