Ralstonia is a genus of primarily environmental gram negative bacteria which are closely related to Burkholderia. ^{Reference Rodriguez-Saldaña, Chiroque-Zavala and Quindes-Jaimes1–Reference Ryan, Pembroke and Adley3} They are relatively avirulent, but often antibiotic-resistant, and they are increasingly recognized as causing outbreaks and pseudo-outbreaks related to contamination of sterile aqueous solutions used in hospitals. ^{Reference Rodriguez-Saldaña, Chiroque-Zavala and Quindes-Jaimes1–Reference Alp, Okalin and Eren-Kutsoylu51} The outbreak described by Luna-Vilchez et al. in this issue of ICHE provides a new example due to Ralstonia picketii contamination of commercially prepared injectable dexmedetomidine vials, linked by whole genome sequencing (WGS) to outbreaks caused by different injectable products in the UK, Germany and Australia. ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5–Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7,Reference Marris, Latham and Swift41} These multi-country outbreaks with different products illustrate the problems associated with the growing complexity of global pharmaceutical supply chains. ^{Reference Saunders, Weaver and Stretch6,Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7,Reference Marris, Latham and Swift41,Reference Sandfort, von Laer and Kampmeier45}

The continued reporting of Ralstonia outbreaks—and the likelihood that many more exist but remain unpublished—raises the question of what infection prevention and control (IPAC) professionals can do to minimize their impact, while regulators work on increasing the microbiologic safety of injectables and other solutions which should be sterile.

In most hospitals, clinical isolates of Ralstonia spp. are very rare, with fewer than one clinical isolate per year. ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5,Reference Saunders, Weaver and Stretch6,Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7,Reference Barbut, Kosmann, Lalande, Neyme, Coppo and Gorin10,Reference Forgie, Kirkland, Rennie, Chui and Taylor11,Reference Gröbner, Heeg, Autenrieth and Schulte13,Reference Fabricci, Trinca and Talotti36,Reference Pellegrino, Schirmer, Velasco, de Faria, Santos and Moreira53} Occasional community-acquired bacteremias occur in persons who inject illicit drugs, and the airways of individuals with advanced cystic fibrosis may become colonized with Ralstonia spp. ^{Reference Zellweger, Bodmer, Täuber and Mühlemann54–Reference Green, Bright-Thomas, Kenna, Turton, Woodford and Jones56} In contrast to rarity in human-derived samples, Ralstonia are very common in aquatic environments. ^{Reference Rodriguez-Saldaña, Chiroque-Zavala and Quindes-Jaimes1} As noted by Luna-Vichez et al., Ralstonia are able to pass through the 0.2 micron filters often used to sterilize aqueous solutions, ^{Reference Rodriguez-Saldaña, Chiroque-Zavala and Quindes-Jaimes1,Reference Gröbner, Heeg, Autenrieth and Schulte13,Reference Hahn57} and also able to grow across a wide range of temperatures, to tolerate low nutrient conditions, and to form biofilms. ^{Reference Ryan, Pembroke and Adley3,Reference DAlessandro, Nusca and Napoli4,Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7} It is perhaps not surprising, then, that a steady stream of outbreaks and pseudo-outbreaks due to Ralstonia spp. have been published over the last 40 years. A 2006 review identified 27 descriptions, beginning in 1982. ^{Reference Ryan and Adley2} In the 20 years since that review, at least 48 reports of 44 outbreak investigations involving Ralstonia spp. have been published (Table 1). ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5–Reference Chen, Huang and Chen52}

Table 1.

Hospital outbreaks of infection due to Ralstonia spp. reported in which sources of infection were identified, 2005–2026 ^a

Table 1. Long description

A table detailing hospital outbreaks of Ralstonia spp. infections, categorized by source, number of outbreaks, species involved, and references. The table has five columns: Source, Number of outbreaks, Source (number of outbreaks), Species (n), and References. The sources are divided into five categories: Commercially manufactured sterile solutions/products, Commercially manufactured non-sterile solutions, In-hospital prepared sterile solutions, Medical/non-medical devices, and Dialysis machines. Each category lists specific sources of infection and the number of outbreaks associated with each. The species column lists the types of Ralstonia involved in each outbreak. The references column provides citations for each outbreak. Row 1: Commercially manufactured sterile solutions/products, 18, Saline vials, ampoules or bags (6), Injectable medication (8) including fentanyl (2), dexmedetomidine (1), dexamethasone (1), hydro-morphine/fentanyl (1), methotrexate (1), magnesium (1), lyophilized urokinase (1), Water (1), Contents of blood gas syringes (2), Wet surfaces of leaking sterile saline bags (1), R. pickettii (13), R. mannitolytica (3), R. insidiosia (2), R. flatus (1), R. solanacearum (1), References include 6,7,18,32,33,41,42,45,52,5,16,17,27,31,36,39,40,50. Row 2: Commercially manufactured non-sterile solutions, 1, Cosmetic water spray, R. mannitolytica (1), References include 44,46. Row 3: In-hospital prepared sterile solutions, 4, Sterile or distilled water (3), Heparin flushes (1), R. pickettii (2), R. mannitolytica (2), References include 23,46,47, 8. Row 4: Medical/non-medical devices, 6, Vapotherm (2), ECMO (2: 1 temperature control unit, 1 single use water heater), Filter on water tap (1), Water bath for heating infant formula (1), R. pickettii (3), R. mannitolytica (3), References include 12,15, 11,34, 35, 49. Row 5: Dialysis machines, 3, Reprocessing machines (2), Faulty reverse osmosis machine (1), R. pickettii (1), R. mannitolytica (1), R. insidiosia (1), References include 24,28, 25.

^a Of 43 clusters identified and investigated, 32 described outbreaks with sources identified and are shown in the Table. For seven outbreaks a source could not be identified. ^{Reference Kismet, Atay and Demirkaya9,Reference Gröbner, Heeg, Autenrieth and Schulte13,Reference Mikulska, Durando and Pia Molinari14,Reference Lucarelli, Di Domenico and Toma21,Reference de Souza, Palmeiro and Maestri22,Reference Rajendran, Sundaramoorthy and Sethuraman29,Reference Çelen, Zhumatayev and Yalçın38} In 2 clusters (each of 3 isolates) ^{Reference Liu, Yan, Zhang, Li, Yang and Li19,Reference Wu, Collier and Crosby37} the isolates were unrelated by WGS or PFGE (in one other outbreak, a single isolate of R. pickettii was unrelated to others), and there were 2 pseudo-outbreaks (one related to sonication of resected prosthetic joint components prior to culture, ^{Reference Edwards, Somayaji, Missaghi, Chan and Bois20} and one related to attempted disinfection of blood culture bottles with a disinfectant solution diluted in tap water). ^{Reference Barbut, Kosmann, Lalande, Neyme, Coppo and Gorin10}

^b One outbreak reported 9 isolates of R. pickettii (highly related by WGS) and one isolate of R. flatus ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5} , and two were predominantly due to R. mannolytica but also included isolates of R. picketii. ^{Reference Fabricci, Trinca and Talotti36,Reference Nannapaneni, Rameshbabu, Sundaramoorthy and Sethuraman46}

^c–gThree outbreaks were each described in two different publications (references Reference Lai, Shen and Chien18 and Reference Chen, Huang and Chen52, Reference Forero, Blanco and Martinez-Vernaza27 and Reference Viana-Cárdenas, Triana, Cárdenas-Álvarez, Carvajal-Diaz, Mendoza and Viasus40, and Reference Pillonel, Blanc and Jacot44 and Reference Cancela Costa, Blanc and Bertelli48) and one in four publications (references Reference Saunders, Weaver and Stretch6,Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7,Reference Marris, Latham and Swift41 and Reference Sandfort, von Laer and Kampmeier45).

Outbreaks of Ralstonia spp. are predominantly associated with positive blood cultures (often drawn from central venous access devices (CVADs)), and most cases occur in intensive care, hematology/oncology or transplant units. Although the case fatality rate is low, Ralstonia spp.’s resistance to antibiotics may delay effective therapy, ^{Reference Rodriguez-Saldaña, Chiroque-Zavala and Quindes-Jaimes1} and numerous publications document that successful therapy may require removal of infected CVADs. ^{Reference Kismet, Atay and Demirkaya9,Reference Gröbner, Heeg, Autenrieth and Schulte13,Reference Bedir Demirdag, Ozkaya-Parlakay and Bayrakdar33,Reference Çelen, Zhumatayev and Yalçın38,Reference Chen, Huang and Chen52}

Strikingly, 18 of the 42 outbreaks reports published in the last 20 years (including 14 of 21 with identified sources reported in the last 5 years) document outbreaks associated with commercially supplied sterile solutions (Table 1). ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5–Reference Chen, Huang and Chen52} Of course, outbreak reports are a biased view of overall occurrence, and larger, longer outbreaks are more likely to be reported. Nonetheless, it is of concern that the median number of cases associated with these outbreaks was 13 (range 2–66) and the median duration was 12 (range 1–56) weeks.

There are a number of barriers to the rapid investigation and management of Ralstonia spp. outbreaks. Isolates are sufficiently rare that they may not be on microbiology and IPAC department lists of sentinel organisms requiring investigation of single cases. ^{Reference Block, Ergaz-Shaltiel and Valinsky15} Until recently, most hospitals would have trusted commercial sterile solutions to be sterile and would investigate other potential sources first. Most often, contamination is not specific, and at relatively low concentrations, such that attack rates may be low for any particular product (22%, 32% and 34% in outbreaks reporting data), ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5,Reference Bedir Demirdag, Ozkaya-Parlakay and Bayrakdar33,Reference Chen, Huang and Chen52} and 2–3 weeks may pass between infections. ^{Reference Kimura, Calvet and Higa8,Reference Sebastian, Gupta and Banerjee47,Reference Alp, Okalin and Eren-Kutsoylu51} In addition, most hospitals do not track particular lot numbers of frequently used products such as sterile normal saline, and it may not be possible to identify which lot was given to a particular patient. Microbiology and IPAC departments may not have previously needed procedures for culturing sterile solutions, and the low concentrations of bacteria present mean that multiple specimens of each lot and product may need to be tested. ^{Reference Ross, Steinmann and Buer16,Reference Lai, Shen and Chien18,Reference Bedir Demirdag, Ozkaya-Parlakay and Bayrakdar33} Finally, presumably because of the combination of limited virulence and the ability to form biofilm, patients may not present with infections until several days after their exposure to contaminated medications. Thus infections may continue to be diagnosed after the contaminated lot of medication is no longer being used. In one outbreak involving saline lock solutions for CVADs, one infection occurred 31 days after exposure to the contaminated lot, ^{Reference Menekşe, Hacıseyitoğlu, Süzük Yıldız and Bayrakdar32} and in another, new cases continued to appear for 16 days after the contaminated solution was withdrawn. ^{Reference Menekşe, Hacıseyitoğlu, Süzük Yıldız and Bayrakdar32}

Nonetheless, recognition of these barriers and consideration of the experiences of existing outbreak investigations should assist IPAC teams in reducing the size and duration of outbreaks. MALDI-TOF now reliably identifies Ralstonia spp, and any clinical isolate of a Ralstonia spp. should generate an investigation (Figure 1). Isolates from ICUs in patients with CVADs are most likely to be bacteremias if an injectable sterile solution is the source, while respiratory or wound isolates are more likely to be associated with solutions or devices used for respiratory/skin care. Isolates from patients cared for in hemodialysis units may be either medication-associated or associated with contamination of water sources for dialysis. The few studies of Ralstonia spp colonizing or infecting persons with cystic fibrosis have not identified injectables or sterile solutions as sources, but have also not investigated the potential for such outbreaks. ^{Reference Coward, Kenna, Woodford and Turton55,Reference Green, Bright-Thomas, Kenna, Turton, Woodford and Jones56}

Figure 1.

Actions to consider when Ralstonia spp. is isolated from a clinical specimen.

In four of the 18 sterile solution outbreaks (and 1 additional outbreak traced to contamination of a non-sterile water spray), cases were identified at multiple hospitals: asking other hospitals to watch for cases may help in identifying which products to investigate. Finding, removing and (if necessary) replacing lots of non-sterile mouth, respiratory, and skin care products used in the involved care unit removes some potential sources of infection easily. Asking whether any solutions are prepared in pharmacy, what non-sealed water baths are present in the unit, and whether anyone might have mistaken distilled water for sterile water in solutions being used can identify other potential risks that can be promptly mitigated. However, the actions most likely to identify a source are to ask about new lots or suppliers of injectable or other sterile solutions and to record which solutions—and if possible what lots of them—have been used in care for the affected patient. Collecting a sample of the lots of saline and injectable medications used for the patient (and if that is not possible, each of the lots commonly used in the ICU) is valuable: in several outbreaks, products and/or lots of products suspected to be the source were no longer available after several cases resulted in an investigation. Replacing existing lots (with quarantine to permit future use if cultures are negative) whenever possible avoids on-going new exposure and cases while the investigation continuess. This is of particular value because the need to perform multiple cultures of different sources may extend the duration of the investigation.

Setting up systems for identifying and recording lots of different solutions used for each patient, and culturing solutions, are more time-consuming and might be considered only if a second infection is identified. However, it may be useful to have the microbiology laboratory prepared to implement cultures. Methods for culturing sterile solutions in reported outbreaks varied from direct plating onto a variety of solid media, ^{Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7,Reference Liu, Yan, Zhang, Li, Yang and Li19,Reference Fabricci, Trinca and Talotti36,Reference Alshuhri, Alosaimi and Alnafee42,Reference Cancela Costa, Blanc and Bertelli48} to inoculation into nutrient broth prior to plating, ^{Reference Aranas, Demot and Cajulao28,Reference Burzyńska, Tukendorf, Fangrat and Dzierżanowska-Fangrat49} to filtration with 0.45 or 0.2um filters prior to plating or incubation in broth, ^{Reference Kimura, Calvet and Higa8,Reference Barbut, Kosmann, Lalande, Neyme, Coppo and Gorin10,Reference Jhung, Sunenshine and Noble-Wang12,Reference Ross, Steinmann and Buer16,Reference Sandfort, von Laer and Kampmeier45} to pharmacologic methods for water sterility testing. ^{Reference Rajendran, Sundaramoorthy and Sethuraman29} In two investigations, samples were culture negative by direct plating, but positive when 10 ml samples were added to blood culture bottles. ^{Reference Fabricci, Trinca and Talotti36,Reference Alshuhri, Alosaimi and Alnafee42} Few outbreaks describe the number of samples processed, but in those that did, 1/10 (10%), 3/16 (19%) and 5/10 (50%) of samples were reported as positive. ^{Reference Ross, Steinmann and Buer16,Reference Lai, Shen and Chien18,Reference Bedir Demirdag, Ozkaya-Parlakay and Bayrakdar33} Typing of even one clinical isolate by WGS permits comparisons to strains from previously reported outbreaks, which may also assist in the identification of products. ^{Reference Luna-Vilchez, Santiago Abal and Aguirre Chávez5–Reference Krone, Rauschenberger, Blaschke, Claus, Kurzai and Kampmeier7}

Ralstonia spp. are, of course, not the only source of outbreaks due to contaminated medication and care products. The closely related genus Burkholderia also causes outbreaks due contaminated injectable medications and sterile saline in vulnerable patients with CVADs in ICUs or NICUs, as well as pseudo-outbreaks. ^{Reference Shaban, Sotomayor-Castillo and Nahidi58,Reference Tavares, Kozak, Balola and Sá-Correia59} However, Burkholderia spp. are also resistant to commonly used antiseptics and have the capacity to metabolize parabens and many other compounds. ^{Reference Shaban, Sotomayor-Castillo and Nahidi58–Reference Doran, Foster and Saunders60} This means that, in contrast to Ralstonia spp., Burkholderia frequently cause outbreaks associated with contamination of non-sterile pharmaceutical and personal care products, ranging from docusate to baby wipes to mouthwash. They frequently contaminate non-sterile ultrasound gel, and have also been reported to contaminate sterile lots. As with Ralstonia, if a single specimen from a non-CF ICU patient yields Burkholderia spp., and investigation should ensue. ^{Reference Doran, Foster and Saunders60}

Other recent outbreaks due to contaminated injectable medications highlight the need for IPAC teams to be alert to the potential for other species to be linked to medication administration. The finding of NDM-producing Escherichia coli colonization/infection associated with contamination of capsules containing cloxacillin manufactured in India demonstrates that contamination may be of carriers and dry products. ^{Reference Agergaard, Porsbo and Sydenham61} The recent identification of candidemias due to Candida wiswanathii in multiple hospitals in Italy associated with contaminated vials of injectable milrinone, also manufactured in India, is a reminder that, although Ralstonia and Burkholderia are the most common microbes associated with outbreaks due to contaminated aqueous solutions, other environmental bacteria and fungi can also be sources. ^{Reference Mesini, Di Pilato and Contu62} Being alert to unusual pathogens causing infections in vulnerable patients—particularly bloodstream infections in ICUs—may offer opportunities to prevent infection.