Significance of polymicrobic bacteriuria in a teaching hospital in Trinidad

To compare microbial prevalence (mixed versus pure), define microbial combination in mixed urine cultures among inpatients and outpatients and to identify factors that might allow a more objective interpretation of polymicrobic urine cultures.

Case series.

The study involved inpatients (hospitalized) and outpatients (those attending outpatient clinics and the accident and emergency department) of the San Fernando General Hospital in southern Trinidad.

Prevalence rates of bacterial isolates in mixed and pure cultures of urine specimens were determined using standard techniques and Kirby-Bauer disc diffusion methodology.

The results obtained showed that of 5,089 urine specimens, 1,491 (29.3%) yielded positive cultures. Of these positive cultures, 524 (35.1%) revealed significant polymicrobic bacteriuria. Eighty five percent yielded two organisms, 13.2% had three organisms and 1.8% had four organisms. Repeat cultures in 157 patients revealed the same organisms in only 57.3% of them. Almost all of the repeat cultures were from patients with in-dwelling Foley catheters. E. coli was the most common single isolate (42.8%), while Klebsiella, Enterobacter and Proteus organisms were most often encountered in mixed cultures. All isolates were relatively sensitive to routinely used antibiotics for urinary pathogens.

The prevalence rate of polymicrobic bacteriuria at our institution was 10.2%. More than 65% of positive cultures were from patients with Foley catheters on open drainage (inpatients) and closed drainage (outpatients). Most were men with out-flow obstruction who either refused surgery, were unfit for surgery, or had to wait long periods to be booked for surgery. No cases developed bacteremia secondary to bacteriuria. All urinary isolates were susceptible to routinely used antimicrobial agents.