This retrospective study was conducted at the University of Tokyo Hospital, a 1217-bed tertiary-care teaching hospital in Tokyo, Japan. Patients with acute biliary tract infection who also had E. coli isolates detected in their blood were included in the study from April 2013 to February 2015. Each patient in this study was included only once, even if the patients repeatedly suffered E. coli bacteremia with acute biliary tract infection. Patient data, including clinical symptoms and microbiological data were collected from the medical records.
Data collection and definitions
Patient data collected included age, sex, underlying disease (diabetes mellitus, malignancy with or without metastasis, lymphoma, and collagen disease), use of immunosuppressants, biliary tract abnormalities, such as insertion of an intrabiliary stent or surgery for biliary carcinoma, gastrointestinal tract abnormalities, and past history of acute biliary infection and bacteremia. History of residence in a nursing home and antibiotic use within three months before onset of bacteremia was also noted. Collected patient laboratory data included white blood cell counts, platelet counts, total bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma glutamyltransferase, and C-reactive protein. Cases in which E. coli was detected from blood cultures obtained within 48 h after admission were defined as community acquired infection. Others were considered hospital acquired infections.
Biliary tract infection was defined according to the Tokyo guideline (28). Cholangitis was defined in cases where all the following sings were positive: 1) generalized inflammation sign such as fever (more than 38.0 °C), elevation of inflammation indicators in blood tests (white blood cell counts less than 4000/mL or more than 10,000/mL, and C-reactive protein 1 mg/dL or more), 2) signs of bile stasis such as jaundice (total bilirubin 2 mg/dL or more), elevation of liver function and biliary function tests (more than one-and-a-half times of the upper limit for normal values for alkaline phosphatase(ALP), gamma-glutamyltransferase(g-GTP), aspartate aminotransferase(AST), or alanine aminotransferase(ALT), normal range; ALP 106-322 U/L, g-GTP 13-64 U/L in men and 9-32 U/L in women, AST 13-30 U/L, ALT 10-42 U/L in men and 7-23 U/L in women, respectively), and 3) imaging of biliary tract abnormalities, such as dilatation of the biliary tract or the presence of a stent, and constriction. Cholecystitis was defined as: 1) localized clinical signs such as Murphy’s sign and pain in right upper abdomen, 2) generalized inflammation such as fever and elevation of inflammation indicators in blood tests, and 3) typical findings, such as acute cholecystitis with echocardiography or CT scan. Severity was divided using the Pitt bacteremia score (29) as severe (score of 2 or more) and non-severe (score less than 2).
All isolates were identified using the Walkaway system (Siemens, Berlin, Germany) or matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (using the MALDI Biotyper; Bruker Daltonik, Germany).
Assignment of E. coli isolates to phylogenetic groups, such as A, B1, B2, C, D, E, and F, was determined by the quadruplex polymerase chain reaction (PCR) method as described by Clermont et al (30). For rapid identification of E. coli sequence types (STs) 69, 73, 95, and 131, the multilocus sequence typing PCR method (31) was performed. The prevalence of 20 virulence factors (papC, sfaD/E, CNF1, iucD, afaB/C, hlyA, tcpC, fyuA, cvaC, fimH, iutA, ibeA, iha, ompT, kpsMT2, papG2, usp, ironEc, sat, and traT) were screened by multiplex PCR using extracted E. coli genomic DNA according to previous reports (32-38).
The two-tailed Fisher’s exact test was used for analysis of categorical data. Non-parametric data were analyzed using the Mann-Whitney U test. Values of P <0.05 were considered significant. All statistical analyses were performed using JMP Pro version 11 software (SAS Institute, Cary, NC, USA).
This study was approved by the research ethics committee at the University of Tokyo Hospital. Obtaining written informed consent from each patient was waived because it was an observational retrospective study. The data were analyzed anonymously.