Kerr, JR

Webb, CH

English

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The Ulster Medical Journal, Volume 61, No. 2, pp. 163 - 165, October 1992.Five cases of Alcaligenes pseudobacteraemiaJ R Kerr, C H WebbAccepted 7 July 1992.SUMMARYA cluster of five cases of pseudobacteraemia due to the organism Alcaligenesdenitrificans occurred in three hospital medical wards over a four week period.The same organism was isolated from four of twelve commercially preparedbottles for erythrocyte sedimentation tests. The most likely explanation for theoutbreak is that the ESR bottles were filled prior to inoculation of blood culturebottles. The outbreak was brought to an end by advising on correct procedure.INTRODUCTIONPseudobacteraemia means false - positive bacteraemia, and it implies contamin -ation of the blood culture medium, usually from an environmental source. Asopportunistic pathogens become more common it is increasingly difficult todistinguish pseudobacteraemia from true pathogens in blood culture. We describea cluster of five cases of pseudobacteraemia due to the organism Alcaligenesdenitrificans over a four week period, occurring in three adjacent hospital medicalwards. A case cluster can suggest an outbreak of infection, but since this organismis known to exist in the environment an investigation to identify a possible sourcewas carried out.METHODSInoculated blood culture bottles are incubated at 37°C and sampled for bacterialgrowth at intervals using a semi -automated blood culture system. If growth isdetected, a sample of the blood culture is aseptically withdrawn from the bottlefor gram staining and subculture on solid media. Routinely, these plates are alsoincubated at 37°C, but once an organism suspected of being an Alcaligenesspecies was isolated, culture plates were incubated at 30°C, which improvedrecovery.Informal discussions with junior medical staff failed to reveal any breach ofblood sampling protocols. In view of previous reports of pseudobacteraemiatraced to contamination of the bottles used for full blood picture and erythrocytesedimentation rate tests, we tested four of each of these bottles from each of thethree medical wards involved. The haematology bottles tested are commerciallymanufactured by Sherwood Medical, UK. They are made of glass and eachcontains 0 5 ml sodium citrate. They are designed to take 4 5 ml blood and areThe Ulster Medical Society, 1992.Department of Bacteriology, Royal Group of Hospitals, Belfast BT12 6BA.J R Kerr, BSc, MB, Registrar in Bacteriology.C H Webb, MB, BDS, FRCPath, Consultant Bacteriologist.Correspondence to Dr Kerr.The Ulster Medical Journalgamma -irradiated at the end of production to ensure sterility. The ESR bottlestested are commercially manufactured by Sterilin, UK. They are plastic and eachcontains 0-4 ml of sodium citrate. They are designed to take 2 ml blood and areprepared under aseptic conditions although not irradiated. From both the haema-tology and the ESR bottles, 20p1 of contained sodium citrate was plated onto blood and MacConkey agars. A gentamicin disk was placed on each plateto screen for any gentamicin-resistant, gram-negative organisms, since theA. denitrificans stain had consistently exhibited this characteristic.Antibiotic sensitivity testing was performed using the Stokes method withPseudomonas aeruginosa National Collection of Type Cultures 10662 (CentralPublic Health Laboratory, Colindale Avenue, London) as a control organism.Isolates were incubated on blood agar at 30°C for 48 hours. Identification wasperformed using the API 20NE system (BioMerieux, France) for non-entericgram - negative bacilli. This is a commercially prepared, semi -automated methodusing a plastic strip containing twenty capules; the capules contain the necessaryreagents for twenty different biochemical tests. A suspension of the test organismis inoculated into each of the capules and the results read after forty - eight hours.RESULTSAll five strains isolated from blood cultures had the same biochemical profileon testing with the API 20NE system, and were identified as Alcaligenesdenitrificans. All had a similar antiobiotic sensitivity profile, being resistant togentamicin and amikacin, and sensitive to netilmicin, ciprofloxacin, aziocillin andceftazidime.Twelve haematology bottles were tested and no bacteria were isolated. TwelveESR bottles were tested, four from each of the three wards, and of these fourgrew a gram - negative, cytochrome oxidase -positive bacillus which was resistantto gentamicin on the primary culture plates. Of the four positive ESR bottles, twocame from one ward and one each from the other wards. The full biochemicaland antibiotic sensitivity profiles of these isolates were similar to that of the bloodculture strains (Table).TABLEIsolates from ESR bottlesAlcaligenes denitrificansResistant Sensitive Variablegentamicin ceftazidime netilmicinamikacin ciprofloxacin aziocillinDISCUSSIONAn organism similar to that which caused five episodes of pseudobacteraemiawas isolated from the ESR bottles available in each of the three wards. Gram-negative organisms have frequently been isolated from haematology and ESRbottles, and these contaminated bottles have been shown to be the cause ofpseudobacteraemia.1 2, 3,4 In these cases, the most likely route of contamination© The Ulster Medical Society, 1992.164Pseudobacteraemia 165has been that after drawing blood from the patient the syringe needle wasremoved and the ESR bottle filled before the blood culture medium wasinoculated. Even if a new sterile needle was placed on the syringe before theblood culture bottles were inoculated, the syringe nozzle could already have beencontaminated during filling of the ESR bottle. This contamination might occureither by direct contact with the inside of the ESR bottle or by aerosol.Successful sampling of blood for culture requires a careful technique withattention to detail. The operator's hands should be washed and gloves may beworn. Various recommendations have been made for skin disinfection of thechosen venepuncture site. Gillies5 advocated a soap and water wash followed byalcohol and povidone iodine, whereas Tyrrel et a16 advise two applications of70% alcohol or an alcohol -based disinfectant. It is essential that alcohol isallowed to evaporate to dryness and iodine, if used, is allowed two to threeminutes to act. After disinfection the operator should not touch the venepuncturesite. Following sampling the needle should be changed prior to inoculation of theblood culture bottles. It is helpful if an assistant is available to rip off the protectivecap from the blood culture bottles and disinfect the diaphragm with an alcoholwipe. If additional blood samples for other tests are also required, the extra bottlesshould be filled after blood culture inoculation to avoid possible contaminatingorganisms from them being carried over to the blood culture bottles. While thedoctors who inoculated the blood culture bottles did not feel that contaminationof this type had occurred, the outbreak was brought to an end by advising on thecorrect procedure.Pseudobacteraemia is an important phenomenon in terms of patient well - being,clinical and laboratory workload, and the cost of unnecessary treatment. Fortun-ately, none of our cases were treated unnecessarily with antibiotics becausemonitoring in the bacteriology department raised the suspicion of pseudobacter-aemia at an early stage.REFERENCES1. Whale K. Pseudobacteraemia: a bedside fault. Lancet 1983; 1: 830.2. Cookson BD, Mehtar S, Sadler G. Serratia pseudobacteraemia. Lancet 1982; II: 1276-7.3. Willson PA, Petts DN, Baker SL. An outbreak of pseudobacteraemia. Br Med J 1981; 283: 866.4. Ispahani P, Lewis HJ, Greaves PW. Pseudobacteraemia, again. Lancet 1985; II: 383-4.5. Gillies RR. Blood culture. In: Gillies RR, Dodds TC. Bacteriology illustrated. Edinburgh: ChurchillLivingstone, 1984: 129-31.6. Tyrrel DAJ, Phillips I, Goodwin CS, Blowers R. The use of the laboratory in diagnosis, therapy andcontrol. London: Edward Arnold, 1979: 312-3.© The Ulster Medical Society, 1992.

5 CASES OF ALCALIGENES PSEUDOBACTEREMIA

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