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Outbreak of Francisella novicida Infections Among Occupants at a Long-Term Residential Facility - Louisiana, April-July, 2011 (Report)

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  • Outbreak of Francisella novicida Infections Among Occupants at a Long-Term Residential Facility - Louisiana, April-July, 2011 (Report)

    Louisiana Morbidity Report
    January - February 2012

    Excerpt:

    Outbreak of Francisella novicida Infections Among Occupants at a Long-Term Residential Facility - Louisiana, April-July, 2011

    Julie Hand, MSPH; Christine Scott-Waldron, MSPH; Gary Balsamo, DVM MPH & TM

    In May 2011, the Infectious Disease Epidemiology Section (IDES), Office of Public Health, was notified of two cases of bacteremia among two individuals at a long-term residential facility in the state.

    Blood culture results identified Francisella tularensis as the causative agent. F. tularensis causes tularemia and is currently classified as a potential bioterrorism agent by the Centers for Disease Control and Prevention (CDC). Samples were sent to the Louisiana State Public Health Laboratory for confirmatory testing and were positive on polymerase chain reaction (PCR) assay but negative by direct fluorescent antibody (DFA).

    These conflicting results indicate the infections could have been caused by F. novicida which is closely related to F. tularensis, and considered a subspecies by some microbiologists. F. novicida is rarely associated with human illness despite the close genetic relationship to F. tularensis.

    Samples were forwarded to the CDC Bacterial Diseases Branch, Division of Vector-Borne diseases (DVBD) for further analysis. F. novicida was confirmed; through pulse field gel electrophoresis (PFGE) it was found that the two isolates were genetically identical strains. F. novicida is an unusual pathogen that has not been known to readily cause human illness; two concurrent cases have never before been identified. An investigation was undertaken to explore possible exposures at the residential facility.

    Active surveillance for additional cases was also initiated.

    Both patients exhibited end-stage liver disease, but their clinical presentations differed at the time of hospital admission. The first patient was hypothermic and unresponsive, with ulcerated lesions of the hard palate and abdominal tenderness. Despite initial improvement when treated with broad spectrum antibiotics, the patient died 11 days after hospitalization. The second patient presented with fever and ascites, and recovered. The dates when the positive blood cultures were drawn were April 4th and 12th. Both patients had a history of chronic underlying medical conditions and multiple visits to the infirmary of the facility, making it impractical to determine an exact date for illness onset.

    After an extensive review of records and an interview with the surviving patient, no common exposure or source was identified.

    Through enhanced surveillance, a third case was identified in July. PFGE results showed that the third isolate differed from the other two by only a single band. The third patient had been on long-term immunosuppressive medications for an underlying illness and the clinical presentation included only knee pain; he also recovered. It was also difficult to determine the exact onset date for the third patient because he had a history of multiple visits to the infirmary for fever in April and also a previous hospital admission in May.

    In August 2011 IDES requested CDC assistance with the investigation.

    The objectives of the Epi-Aid were to:

    • Systematically review the records of the three cases
    • Explore all possible common exposures including food, water
    and environmental sources
    • Investigate the possibility of laboratory contamination
    • Collect environmental samples for testing
    • Recommend a protocol for enhanced surveillance.

    Medical charts and infirmary records for all three infected patients were reviewed in detail, along with information on all locations they had been within the facility since March. In-person, open-ended interviews were conducted with the two surviving patients.

    All three patients were African-American males with a mean age of 45 years. No single medical procedure or medication was common to all three patients. In the month prior to diagnosis, the three patients were housed in separate units and had no contact with each other. Food sources at the facility included dining hall kitchens, a canteen and a café. There was no common exposure from these three entities identifi ed as unique to these three patients. There is a farm on-site, and the processing and handling of vegetables was also ruled out as a potential exposure. Records documented that none of the three patients were working in the month prior to infection onset. Interviews with the two surviving patients revealed that one reported infrequent exposure to rodents, but neither had indicated exposure to other animals or insects. Both patients stated that they consumed large quantities of water and relied on water instead of other beverages available within the facility. Both reported consuming ice directly, or with water. No significant events were detected in the water system during the period of interest. Water at the facility is supplied through the parish water system, and is monitored closely on a routine basis. There are 15 ice machines within the facility. Four are located inside a building near the infirmary and the other 11 are housed in an open-air enclosure. Environmental samples of the water supply and ice machines were obtained and analyzed at CDC DVBD.

    To rule out laboratory contamination as a possible explanation for these three cases, record reviews and interviews with the microbiologists at the hospital were completed. No other isolates of Francisella were identified and there were no instances where unidentified Gram-negative rods had been isolated. During a five month period, the hospital processed 1,981 blood culture sets of which 136 (6.9%) were from patients at the facility of concern. Based on these values, the probability that random contamination at the hospital would occur only among cultures obtained from this facility is estimated at p<0.001.

    Among the environmental samples obtained and analyzed by CDC DVBD, swabs from one set of ice machines yielded evidence of F. novicida by PCR. Although the ultimate source of contamination could not be identified, ice appears to be the likely vehicle of transmission. IDES reviewed guidelines with staff for maintenance and cleaning of ice machines, dispensers and storage chests in addition to proper sanitary handling and transportation of ice. These guidelines can be viewed on the IDES website at http://new.dhh.louisiana.gov/assets/...inesManual.pdf .

    Ice machines at the facility are no longer kept in an open-air enclosure and are routinely cleaned; they are at much lower risk from obvious environmental exposures. Enhanced active surveillance for additional cases continued through January 2012. From early September to mid-December, 2011, no additional cases were identified.

    For more information, please contact Ms. Hand at (504) 568-
    8298 or email to julie.hand@la.gov.

    http://new.dhh.louisiana.gov/assets/...2/janfeb12.pdf
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