Vol 16, No. 28
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Monday, July 28, 1997
A. Provided by Carmela Groves, R.N., M.S., Chief, Division of Outbreak Investigation, Maryland Departent of Health and Mental Hygiene
1 outbreak was reported between June 23rd and June 30th, 1997.
10 outbreaks were reported between June 30th and July 14th, 1997.
8 outbreaks were reported between July 14th and July 21st, 1997.
2 outbreaks were reported between July 21 and July 25, 1997.
B. The Johns Hopkins Hospital: Information provided by Jessica L. Dodge, M.D., Pathology:
Clinical Information: The patient is a 42 year old African American woman with a history of daily intravenous drug use (heroin and cocaine) and a right iliac giant cell tumor which was resected 24 years ago. Two days prior to admission, she awoke with right lower quadrant abdominal pain and right hip pain. She developed nausea, vomiting, fatigue and difficulty walking. She admitted to having recently injected drugs into her right upper thigh.
Physical examination: Temp 102o F; right and left lower quadrant abdominal tenderness; tenderness over the lumbar spinous processes and right iliac crest; bilateral axillary and inguinal lymphadenopathy; multiple needle tracks on upper and lower extremities
Labs: WBC 11,000 with 88 polys, 8 lymphs, 2 monos, 1 band; Hb 12.2; HCT 37.6; Plt 274,000; ESR 60; Hepatitis C antibody positive; Hepatitis B surface antigen negative; HIV negative; Three sets of blood cultures grew Serratia marcescens.
Radiology: MRI of lumbar spine: Enhancement of L3-L4 disc consistent with discitis. Anterior right paraspinal mass consistent with an inflammatory mass centered around L3-L4 region.
Triple phase bone scan: Intense uptake around L3-L4 region suggestive of osteomyelitis.
Echocardiogram: No valvular vegetations
Clinical course: Intravenous therapy with imipenem and gentamicin resulted in defervescence and improvement of pain. The patient was discharged with a Hon catheter for continuation of intravenous antibiotic therapy. The plan is to treat her with six weeks of intravenous antibiotics followed by six weeks of oral antibiotics.
The genus Serratia is a member of the family Enterobacteriaceae. The Serratia species are found in water and soil and on leaves, shrubs, fruits, vegetables, herbs, mushrooms, mosses and insects. The only Serratia species that have been routinely associated with human disease is S. marcescens. There have been rare reports of disease due to S. liquifaciens, S. rubidaea and S. odorifera. Serratia is an opportunist that has been recognized as a human pathogen only since the 1960s. Before that time, the red pigment found in some strains made them attractive as marker organisms to study bacterial transmission. The U.S. Army used Serratia in the 1950s to study population vulnerability to aerosolized bacteria.
Epidemiology: Serratia appears to be less likely to colonize the gastrointestinal tract but more likely to colonize the respiratory and urinary tracts of hospitalized patients. One study of 56 cases of Serratia bacteremia found the most common portals of entry to be lung, genitourinary, unknown, intravenous catheter, gastrointestinal, skin, dialysis fistula and peritoneum via intraperitoneal abscess. Eighty percent of these cases were nosocomial (vs. 21.7% of controls) and 25% were fatal (vs. 13.6% of controls)(4). The predominant mode of transmission appears to be hand-to-hand transmission by hospital personnel. Outbreaks have been traced to colonization of faucets, pressure transducers, medicated solutions and equipment (e.g., bronchoscopes). Among nosocomial infections, Serratia causes approximately 4% of bacteremias and lower respiratory infections and 2% of urinary tract, surgical wound and cutaneous infections. In 1996 at The Johns Hopkins Hospital, Serratia species were isolated from 1.2% of nosocomial bloodstream infections. Most hospital-associated cases are associated with intravenous, intraperitoneal and urinary catheters and instrumentation of the urinary and respiratory tracts. Serratia has been specifically associated with infections in heroin addicts. It accounted for 14% of addict-associated endocarditis in San Francisco in the early 1970s and has been noted as a cause of osteomyelitis in this population. In the outpatient setting, Serratia is notable for causing septic arthritis among patients receiving intra-articular injections for diagnostic or therapeutic purposes. Recently, an epidemic of septic arthritis involving 10 patients was found to be caused by Serratia contamination of a benzalkonium chloride antiseptic used to soak cotton balls. Other reported infections include meningitis, otitis media, lymphadenitis and thyroiditis.
Laboratory Diagnosis: Diagnosis is established by culture of the organism. Serratia species grow well on enriched media (e.g., blood agar) at 35-37o C. They are non-lactose fermenters and are motile. Serratia species produce extracellular DNase at 25o C and gelatinase at 22o C. They elaborate lipase and are resistant to colistin, ampicillin and cephalothin. These properties do not characterize any other Enterobacteriaceae. Not all S. marcescens organisms produce the typical red pigment prodigiosin. S. rubidaea and S. plymuthica elaborate the same water-insoluble compound or a very similar one. The various Serratia species can be distinguished from S. marcescens by decarboxylation and fermentation reactions. Epidemiologic differentiation of S. marcescens can be achieved by biotyping based primarily on carbon sources or by pulsed-field gel electrophoresis.
Treatment: Antibiotic treatment of Serratia is complicated by the high frequency of multiple drug resistance. Many strains are susceptible to amikacin with synergy frequently seen with the addition of carbenicillin or ticarcillin. The newer generation beta-lactam antibiotics as well as the newer quinolones may be particularly useful for aminoglycoside-resistant strains. In 1996 at The Johns Hopkins Hospital, 86% of the Serratia species isolates from nosocomial bloodstream infections were susceptible to cefotaxime and ceftazidime. Seventy one percent were susceptible to ticarcillin and tobramycin and 57% were susceptible to gentamicin and piperacillin. The isolate from the patient presented above was susceptible to ticarcillin (MIC=8), gentamicin (MIC=1) and imipenem.