Antimicrobial resistance patterns in outpatient urinary tract infections – the constant need to revise prescribing habits
To the Editor: We commend the retrospective survey of antimicrobial susceptibility at 3 Military Hospital in Bloemfontein1 and appreciate the concern about very high rates of culture-negative urine received at the laboratory. Possibly many such samples came from patients already receiving antimicrobials. We feel that it would have been better to screen urine samples received for culture for the presence of any antimicrobials in the sample to ensure judicious therapeutic intervention.
Recently, investigators at the Hamad Medical Corporation, Doha, Qatar, carried out antibiotic screening of 1 680 urine samples (employing Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923) that were being processed for culture. There were 2 494 culture-positive urine samples that included 388 samples with antibacterial substances. Among these samples were 345 sterile samples, 32 with insignificant growth samples, and 11 with mixed growth.2
Screening urine samples received at 3 Military Hospital in Bloemfontein1 would not be an insurmountable task. Antibacterial substance screening of urine samples was feasible even more than 40 years ago at the All India Institute of Medical Sciences, New Delhi, India,3 where screening of 426 urine samples was done by employing the standard Oxford strain of S. aureus. There was demonstrable antibacterial activity in 127 samples, accompanied by bacterial growth in 63 samples. Isolates included E. coli – 28 isolates, Klebsiella species – 13, Pseudomonas aeruginosa – 10, Proteus spp. – 6, S. aureus – 3, Alkaligenes faecalis – 2, and Streptococcus faecalis – 1. A history of prior antibiotic use could be obtained in 25 cases only, though there was no relevant information in the laboratory requisition slips. It was also possible in 7 cases to identify the antibiotics being used by the patients. The isolates in the urine samples were resistant in vitro to the prescribed antibiotics. Even with an adequate amount of antibiotic in the urine, there was little benefit to the individual.
Obviously, any sterile culture report on a urine sample from a patient with a demonstrable antibacterial activity could be erroneous unless a subsequent urine culture is found to be sterile. Laboratory personnel would not ignore patients with rather low bacterial counts in any urine sample with concurrent antibacterial activity. Such isolates might represent either a declining population of susceptible bacteria or an ascending antibiotic-resistant bacteria population.
Last but not least, any expenditure for carrying out concurrent screening for antibacterial substances in all urine samples cultured at 3 Military Hospital in Bloemfontein1 or elsewhere would be cost-effective, and will lead to better management of urinary tract infections and would ensure rational disease management.
Sant Parmanand Hospital
1. Bosch FJ, van Vuuren C, Joubert G. Antimicrobial resistance patterns in outpatient urinary tract infections – the constant need to revise prescribing habits. S Afr Med J 2011;101:328-331.
2. Wilson G, Badarudden S, Godwin A. Antibiotic screening of urine culture as a useful quality audit. J Infect Dev Ctries 2011;5(4):299-302.
3. Arya S C. Screening of urine samples for bacteriuria and antibacterial activity. Indian J Medical Sciences 1967;21:715-720.
Dr van Vuuren replies: All urine samples included in our study were processed by the National Health Laboratories Services (NHLS) in Bloemfontein. In line with standard procedure, Bacillus subtilis ATCC 6633 was used to screen for the presence of antibiotics, and a leukocyte count performed on all urine samples sent for culture at the NHLS. If there is no growth of bacteria in the presence of antibiotics, significant numbers of leukocytes warrant further investigation.
As we excluded culture-negative samples from our analysis, we obviously cannot comment on the number of samples with no growth due to the presence of antibiotics. Apart from the possibilities mentioned in our article, antibiotic administration prior to sample collection may be another cause for negative cultures.
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