Sixteen cases of Ralstonia mannitolilytica bacteraemia were detected during the outbreak in the haemodialysis unit at the Steve Biko hospital. Prior to the outbreak, we had no reported isolates of this organism being cultured over the previous year.
All patients presented with fever and rigours whilst undergoing haemodialysis, usually within the first hour of dialysis. The usual patient profile was a patient with an indwelling haemodialysis catheter (no arterio-venous fistulae patients became septic) who had end stage renal disease, complicated by hypertension and mineral bone disease. Empiric antibiotic cover was started with vancomycin and a carbapenem (imipenem or meropenem), as per Steve Biko Academic Nephrology guidelines for line sepsis. This was de-escalated according to the culture and antimicrobial susceptibility results as they became available. In this case, de-escalation to piperacillin-tazobactam was advised if the clinicians decided to continue therapy as all isolates were susceptible to this antibiotic.
All sixteen patients survived except one, who demised after a long hospital stay and many complications. Whilst the mortality was unlikely due to Ralstonia sepsis, the precipitating event was Ralstonia septicaemia. All patients had their dialysis catheters changed, barring one patient who declined the surgery. This patient was given a 2 week course of high dose imipenem whilst on dialysis (i.e. every second day), and the dialysis catheter was locked with imipenem after dialysis. This resulted in good recovery for the patient.
The mean time to the first negative subsequent culture was 13 days in these patients. It should be noted however that during the course of the outbreak, the same water system was used to administer dialysis to these patients. This could have impacted on the duration of blood culture positivity and response to therapy in these patients.
R.mannitolilytica is frequently recognised as a multidrug resistant organism [8]. Daxboeck et al. reported carbapenem resistance in 12 out of their 30 strains [9]. In an Italian study of R.mannitolilytica isolates, no carbapenemase genes were detected but all isolates had phenotypic evidence of AmpC β-lactamases [1]. These enzymes confer a wide resistance to many β-lactam agents such as the cephalosporins, β-lactam- β-lactamase-inhibitor combinations, aztreonam and carbapenems, in case of association with altered porins and/or efflux mechanisms [10]. All isolates in this study were resistant to meropenem, but susceptible to imipenem. Sequencing for detection of resistance genes was not performed.
Environmental organisms, namely Bacillus species and Stenotrophomonas were recovered from water prior to it entering the reverse osmosis pump however these organisms were not found after this point. The reverse osmosis pump probably had some residual effect against these organisms. However, a number of hydrophilic organisms were cultured from water collected after it had passed through the reverse osmosis pump. The contamination at this point may have been through leaks in the reverse osmosis pump which were noted and visible in Fig. 2. The water then passed through the UV light which significantly reduced the numbers of Cupriavadus pauculus and Ralstonia pickettii organisms such that they were not cultured after passage through UV light. Sphingomonas paucimobilis seemed unaffected by UV light and was still cultured after this point although the organism was never cultured from clinical samples. We postulated that Ralstonia species may have survived the UV light and occurred in small numbers, likely below the limit of detection of culture, hence the reason that it was cultured from patient specimens but not from the water samples collected in the wards. An alternative explanation could be that UV treatment resulted in the unculturable state of Ralstonia species, and the host environment with poor immunity would resuscitate these unculturable bacteria.
Laboratory identification may be problematic with Ralstonia species. Ralstonia mannitolilytica shows similar biochemical properties to Ralstonia pickettii [3]. Tests for nitrate reduction (negative in R.mannitolilytica) and acidification of D-arabitol and mannitol (both negative in R.pickettii) can differentiate the 2 species [11]. Matrix assisted laser desorption and ionisation time of flight methods such as MALDI TOF MS (Biomerieux, France) has also been found to yield a more accurate species level identification of Ralstonia species [4]. 16S rRNA gene sequencing has proved very useful in the definitive identification of R.mannitolilytica, and is now considered the reference method for identification to species level [4, 12]. We used the Vitek 2 instrument for identification and this may explain why Ralstonia picketii was identified from the water specimen as opposed to Ralstonia mannitolilytica from clinical specimens. In this case, the banding pattern on ERIC-PCR was identical of the R.picketii cultured from water and the clinical R.mannitoliliytica. In addition, the antibiogram of the R.picketii was also identical to the R.mannitoliliytica. It was for these reasons as well as cost saving reasons that we did not send the R.picketii isolated for species level identification (i.e. 16S rRNA sequencing).
Following the above findings, we contacted the hospital management and advised that the entire dialysis system be overhauled. The recommendation included changing all the piping in the system as Ralstonia species are known to exhibit biofilm formation in plastic water piping [13]. As a minimum, the reverse osmosis pump required urgent repair. It was further advised that the UV lights be checked frequently so as to confirm that they are working at the optimal intensity. It was noted upon enquiry that maintenance of the dialysis water system was lacking with inadequate service records and service contracts. We advised that these should be re-instituted as a matter of urgency.
The hospital management responded positively by repairing the reverse osmosis pump. They also contracted a private company to sterilize the dialysis water system immediately. Another company was contracted to test dialysis water every 3–6 months as per the company policy. These measures proved to be effective as we did not detect any further cases of Ralstonia mannitolilytica bacteraemia at the Steve Biko Hospital after this intervention.
Ralstonia outbreaks usually persist for prolonged periods [1]. The most likely reason for this is that the source of the outbreak is usually hypothesized and not pinpointed in many studies [1]. Daxboeck et al. (2005) reported isolation of R. mannitolilytica in 30 patients attending 15 different wards between February 2002 and March 2004 and in their study, the source of the outbreak was never identified [9]. One of the strengths of this study was the fact that we detected the source of the outbreak and were therefore able to control the outbreak in a matter of 6–8 weeks.
A limitation of this study is that a better method for discriminatory power (such as whole genome sequencing) to determine clonality was not used amongst our isolates. Furthermore we did not determine the antimicrobial resistance genes in the Ralstonia mannitolilytica isolates in this study.
