Urinary Tract Infection in General Practice : Direct Antibiotic Sensitivity Testing as a Potential Diagnostic Method P. G. Scully, ~ B. O'Shea, ~ K. P. Flanagan, ~ F. R. Falkiner. 2
~St. James's Hospital, Dublin 8. 2Department of Clinical Microbiology (Trinity College), St. James's Hospital, Dublin 8. Direct Antibiotic Sensitivity Testing (DST) is a rapid means of diagnosing urinary tract infection (UTI) and obtaining antibiotic sensitivity patterns of the infecting organisms. In this study 227 urine samples from general practice were analysed using this technique and the results obtained were compared with those obtained using the standard laboratory method. DST was shown to be 94.6% sensitive, and 80.7% specific. Escherichia coil was the commonest infecting organism. Augmentin was the most effective antibiotic tested, all organisms tested in vitro, being susceptible. Direct Sensitivity Testing is rapid, inexpensive, easy to perform, highly sensitive and specific. It should be considered by general practitioners as an alternative to the problems and delays involved in sending urine samples to the laboratory and in awaiting the results. Introduction
Mostbusy general practitioners would normally treat one episode of urinary tract infection every day1. Many doctors start antimicrobial treatment empirically, without first obtaining a urine specimen for laboratory examination 2. Ideally, a urine specimen should be sent first; this can involve some effort, and there may be delay before receiving resuits. The correct use of the dipslide is particularly beneficial2 but a possible alternative is the Direct Sensitivity Test (DST). This is a rapid means of detecting infecting organisms in urine, which also indicates their antibiotic sensitivities. DST was introduced in this group of hospitals (the Federated Dublin Voluntary Hospitals and St. James's) in Address for correspondence : Dr. Brendan O'Shea, 55 Cennffort, Dublin 8.
1980. It was developed to meet the need for a system of rapid pre-operative urine testing in order to indicate appropriate antibiotic chemotherapy for patients undergoing transurethtral procedures3. It was felt that DST could be applied in general practice as a rapid cost-effective means of diagnosing UTI, and guiding antibiotic choice. Accordingly, this study was undertaken to determine the sensitivity and specificity of the (modified) DST technique. Methods The original DST technique has been slightly modified in this study, so that it is simpler to perform and less expensive. The technique used was as follows : A clean mid-stream urine specimen (MSU) was obtained and using a cotton-tipped swab dipped in the well mixed sample, it was applied to a DST agar plate, covering the entire surface of the plate twice. Standard antibiotic-containing discs (e.g. 'Multi-discs' - Mast Laboratories, Liverpool) or separate discs applied with a disc dispenser (Oxoid Ltd., Basingstoke) were placed on the plate which was then incubated at 37~ (Figure la, b). The bacterial growth and antibiotic sensitivities could be detected usually not less than six hours later. Normally, susceptibility is defined by a zone around the disc of not less than 1.5 cmm total diameter. In this study, specimens of urine arriving at the Cenlral Pathology Laboratory, St. James's Hospital, from general practitioners were identified and recorded. In order to eliminate bias, DST was performed on those specimens before laboratory results were known. Bacterial growth was recorded the next day in the following categories : 1. No growth. 2. Light growth. 3. Moderate growth. 4. Heavy growth. Antibiotic sensitivities were recorded on all specimens which showed bacterial growth. 98
Laboratory results are normally re. ported in the following four groups : 1 No growth. 2. Insignificant growth (i.e. bacterial count less than 105 per ml). 3. Mixed growth (i.e. growth of contaminant organisms). 4. Significant growth (i.e. bacerial count greater than 105 per ml). The laboratory reported antibiotic sensitivities on the relevant specimens. The results obtained from the DST technique were then analysed in relation to the laboratory results, which were assumed to be 100% accurate. Results and Discussion
During a four week period in March and April 1988, 227 specimens were recorded and analysed. They were received from 90 different general practitioners in the Dublin area and 79% of samples were from femalepatients. The age of the patients was specified on 130 forms only, and ages ranged from 4 months to 96 years. Mean female age was 33~yearsi mean male age 36 years. Of the patients v~ith specified age, 55% were females under 45 years. Laboratory analysis revealed a total of 56 (24.6%) infected urines. The remainder were reported as follows: 54 (23.7%) insignificant; 44 (18.4%) mixed growth and 73 (32.2%) no growth. Using the DST technique a positive result was taken as heavy growth or moderate growth. Samples recorded On DST as (a)no growth and (b) light growth were taken as negative cultures. Fifty-six urine samples were positive in the laboratory. Of these, 53 were positive using DST with only three false negatives. This shows the sensitivity ofDS T to be 94.6% as shown in Table I. There were 171 samples, which on laboratory culture were negative. Of these, 138 were negative on DST, with 33 false positives. These results show a' specificity for DST of 80.7% as shown in Table I.
VoL159
Urinary tract infection 99
No. 4
TABLE I Sensitivity and Specificity of DST
Labortory Negative
Laboratory Positive DST } Positive
Heaavy growth Moderate
DST 1 NegativeJ
Laboratory Negative after Exclusion of 44 Contaminated Specimens
40 13
17 16
(3) (4)
Light growth No growth
2 1
26 112
(16) (104)
TOTAL
56
171
(127)
53 xl00] Sensitivity ofDST { = -56 138 100~ Specificity of DST { = --X 171 TRUE specificity Of DST (after exclusionr 120 100~ of 44 contaminated ~ = - - x specimens) 127
Forty-four specimens were cultured as mixed growths. A mixed growth of organisms very often arises from urine samples which have been allowed to stagnate for some time, allowing proliferation of contaminants 4. There is no reason for delay between collection of urine, and analysis using the DST technique. Therefore, it is more relevant to examine the specificity of DST, having excluded these 44 samples. This is shown to be 94.5% as seen in Table I. Correlation of antibiotic sensitivities was difficult to quantify. This was because the test antibiotics used by the laboratory varied, while those used in DST were a standard eight (ampicillin, cephradine, sulphonamide, trimethoprim, gentamicin, amikacin, nitrofurantoin, cefuroxime). The 53 positive cultures common to both the laboratory and DST techniques, were analysed for antibiotic sensitivity correlation. The number of common antibiotics varied from three to six. Sixty-eight per cent had complete correlation (either 3/3; 4/4; 5/5 or 6/6). A further 23% correlated in all but one of the common antibiotics. No sample showed correlation in less than half the antibiotics tested by both methods.
=
94.6%
=
80.7%
=
94.5%
were sensitive to trimethoprim while the sensitivities to ampicillin and sulphonamide were lower (60% and 53% respectively). Sensitivity to augmentin was tested on 35 infected urines, and all organisms tested were sensitive. See Table II. A detailed study into the economics of DST was not made, but DST is an inexpensive procedure, especially in the saving of technical time. An agar plate may be purchased commercially for approximately 40 pence. Antibiotic
Infecting Organisms The most common pathogen was E. coli (65.5%), followed by Proteus mirabilis and Streptococcus species. This is shown in Table 11. Analysis of the antibiotic sensitivities of the 56 infecting organisms in this study was performed, using the results obtained from the laboratory. Ampicillin, trimethoprim and sulphonamide were the only three test antibiotics used by the laboratory on all the positive cultures. Seventy-eight per cent of isolates
TABLE II Infecting Organisms and their Antibiotic Sensitivities. No. sensitive to:
AUGMENTIN No. No. Tested Sensitive
No.
%
38
65.5
19
33
19
24
24
P. Mirabilis
8
13.8
8
3
7
5
5
Strep. spp.
7
12.1
7
6
2
6
6
Klebsiella & other GNB 3
5.2
1
2
1
Staph. saprophyticus
1
1.7
0
0
1
Staph. epidermis
1
1.7
0
1
1
E. coli
TOTALS
58
100
AMP TMP Sulp
35 45 31 (60%) (78%) (53%)
35
35 (100%)
100 Scully et al.
I.J.M.S.
Apra, 1990
test discs and cotton tip swabs cost little. The main expense involved in setting up for DST in a GP practice would be the initial capital outlay on a suitable incubator. This may cost in the region of s The fact that some 43% of MSUs gave equivocal results in the laboratory tests indicates that there are problems in either collection of the specimens or transport of the specimens to the laboratory. If the urinary dipslide technique is not usedz the DST method is a suitable alternative.
Fig. la - Heavy growth of E. coli resistant only to ampicillin and sulphafurazole.
The DST technique is highly sensitive and specific for demonstrating the presence of infection; and for determining antibiotic sensitivities. DST is also easy to perform, rapid and inexpensive. General practitioners should consider this technique as a viable alternative to the practice of sending urine samples to the laboratory. While providing an accurate diagnostic indicator, routine use of DST for the diagnosis of suspected UTI might eliminate such practical difficulties as transport and delay. DST certainly offers the GP more autonomy in the diagnosis and management of a very prevalent condition.
Acknowledgements We would like to thank the following for their help and encouragement: Mr. L. English, Dr. J. B. Walsh, Mr. Eamonn Kiely, Dr. Donal McSorley and Mrs. Mary Foody who typed the manuscript. References
1. McCue, J. D. Urinary tract infection and dysufia, Post Graduate Medicine 1986: 80, 5, 113-142 2. Murphy, D. M., Gillespie, W. A., Cafferkey, M. T.,Nelson, H. G., Falkiner, F. R., Ruddock, G. Urinary tract infection in female patients - a survey in general practice in the Dublin area. Irish Medical Journal 1982: 75, 240242 3. Cafferkey, M. T., Falkiner, F. R., Gillespie, W. A.0 Murphy, D. M. Antibiotics for the prevention of septicaemia in urology. Journal of Antimicrobial Chemotherapy 1982:9.471 477.
Fig. l b - Moderate g r o w t h of sensitive E. coli with intermediate sensitivity to cephradine.
4. Brumfitt, W., Percival A., Williams, J. D. Estimation of bacteria and white cells in urine. Association of Clinical Pathologists Broadsheet 80, 1973.
~St. James's Hospital, Dublin 8. 2Department of Clinical Microbiology (Trinity College), St. James's Hospital, Dublin 8. Direct Antibiotic Sensitivity Testing (DST) is a rapid means of diagnosing urinary tract infection (UTI) and obtaining antibiotic sensitivity patterns of the infecting organisms. In this study 227 urine samples from general practice were analysed using this technique and the results obtained were compared with those obtained using the standard laboratory method. DST was shown to be 94.6% sensitive, and 80.7% specific. Escherichia coil was the commonest infecting organism. Augmentin was the most effective antibiotic tested, all organisms tested in vitro, being susceptible. Direct Sensitivity Testing is rapid, inexpensive, easy to perform, highly sensitive and specific. It should be considered by general practitioners as an alternative to the problems and delays involved in sending urine samples to the laboratory and in awaiting the results. Introduction
Mostbusy general practitioners would normally treat one episode of urinary tract infection every day1. Many doctors start antimicrobial treatment empirically, without first obtaining a urine specimen for laboratory examination 2. Ideally, a urine specimen should be sent first; this can involve some effort, and there may be delay before receiving resuits. The correct use of the dipslide is particularly beneficial2 but a possible alternative is the Direct Sensitivity Test (DST). This is a rapid means of detecting infecting organisms in urine, which also indicates their antibiotic sensitivities. DST was introduced in this group of hospitals (the Federated Dublin Voluntary Hospitals and St. James's) in Address for correspondence : Dr. Brendan O'Shea, 55 Cennffort, Dublin 8.
1980. It was developed to meet the need for a system of rapid pre-operative urine testing in order to indicate appropriate antibiotic chemotherapy for patients undergoing transurethtral procedures3. It was felt that DST could be applied in general practice as a rapid cost-effective means of diagnosing UTI, and guiding antibiotic choice. Accordingly, this study was undertaken to determine the sensitivity and specificity of the (modified) DST technique. Methods The original DST technique has been slightly modified in this study, so that it is simpler to perform and less expensive. The technique used was as follows : A clean mid-stream urine specimen (MSU) was obtained and using a cotton-tipped swab dipped in the well mixed sample, it was applied to a DST agar plate, covering the entire surface of the plate twice. Standard antibiotic-containing discs (e.g. 'Multi-discs' - Mast Laboratories, Liverpool) or separate discs applied with a disc dispenser (Oxoid Ltd., Basingstoke) were placed on the plate which was then incubated at 37~ (Figure la, b). The bacterial growth and antibiotic sensitivities could be detected usually not less than six hours later. Normally, susceptibility is defined by a zone around the disc of not less than 1.5 cmm total diameter. In this study, specimens of urine arriving at the Cenlral Pathology Laboratory, St. James's Hospital, from general practitioners were identified and recorded. In order to eliminate bias, DST was performed on those specimens before laboratory results were known. Bacterial growth was recorded the next day in the following categories : 1. No growth. 2. Light growth. 3. Moderate growth. 4. Heavy growth. Antibiotic sensitivities were recorded on all specimens which showed bacterial growth. 98
Laboratory results are normally re. ported in the following four groups : 1 No growth. 2. Insignificant growth (i.e. bacterial count less than 105 per ml). 3. Mixed growth (i.e. growth of contaminant organisms). 4. Significant growth (i.e. bacerial count greater than 105 per ml). The laboratory reported antibiotic sensitivities on the relevant specimens. The results obtained from the DST technique were then analysed in relation to the laboratory results, which were assumed to be 100% accurate. Results and Discussion
During a four week period in March and April 1988, 227 specimens were recorded and analysed. They were received from 90 different general practitioners in the Dublin area and 79% of samples were from femalepatients. The age of the patients was specified on 130 forms only, and ages ranged from 4 months to 96 years. Mean female age was 33~yearsi mean male age 36 years. Of the patients v~ith specified age, 55% were females under 45 years. Laboratory analysis revealed a total of 56 (24.6%) infected urines. The remainder were reported as follows: 54 (23.7%) insignificant; 44 (18.4%) mixed growth and 73 (32.2%) no growth. Using the DST technique a positive result was taken as heavy growth or moderate growth. Samples recorded On DST as (a)no growth and (b) light growth were taken as negative cultures. Fifty-six urine samples were positive in the laboratory. Of these, 53 were positive using DST with only three false negatives. This shows the sensitivity ofDS T to be 94.6% as shown in Table I. There were 171 samples, which on laboratory culture were negative. Of these, 138 were negative on DST, with 33 false positives. These results show a' specificity for DST of 80.7% as shown in Table I.
VoL159
Urinary tract infection 99
No. 4
TABLE I Sensitivity and Specificity of DST
Labortory Negative
Laboratory Positive DST } Positive
Heaavy growth Moderate
DST 1 NegativeJ
Laboratory Negative after Exclusion of 44 Contaminated Specimens
40 13
17 16
(3) (4)
Light growth No growth
2 1
26 112
(16) (104)
TOTAL
56
171
(127)
53 xl00] Sensitivity ofDST { = -56 138 100~ Specificity of DST { = --X 171 TRUE specificity Of DST (after exclusionr 120 100~ of 44 contaminated ~ = - - x specimens) 127
Forty-four specimens were cultured as mixed growths. A mixed growth of organisms very often arises from urine samples which have been allowed to stagnate for some time, allowing proliferation of contaminants 4. There is no reason for delay between collection of urine, and analysis using the DST technique. Therefore, it is more relevant to examine the specificity of DST, having excluded these 44 samples. This is shown to be 94.5% as seen in Table I. Correlation of antibiotic sensitivities was difficult to quantify. This was because the test antibiotics used by the laboratory varied, while those used in DST were a standard eight (ampicillin, cephradine, sulphonamide, trimethoprim, gentamicin, amikacin, nitrofurantoin, cefuroxime). The 53 positive cultures common to both the laboratory and DST techniques, were analysed for antibiotic sensitivity correlation. The number of common antibiotics varied from three to six. Sixty-eight per cent had complete correlation (either 3/3; 4/4; 5/5 or 6/6). A further 23% correlated in all but one of the common antibiotics. No sample showed correlation in less than half the antibiotics tested by both methods.
=
94.6%
=
80.7%
=
94.5%
were sensitive to trimethoprim while the sensitivities to ampicillin and sulphonamide were lower (60% and 53% respectively). Sensitivity to augmentin was tested on 35 infected urines, and all organisms tested were sensitive. See Table II. A detailed study into the economics of DST was not made, but DST is an inexpensive procedure, especially in the saving of technical time. An agar plate may be purchased commercially for approximately 40 pence. Antibiotic
Infecting Organisms The most common pathogen was E. coli (65.5%), followed by Proteus mirabilis and Streptococcus species. This is shown in Table 11. Analysis of the antibiotic sensitivities of the 56 infecting organisms in this study was performed, using the results obtained from the laboratory. Ampicillin, trimethoprim and sulphonamide were the only three test antibiotics used by the laboratory on all the positive cultures. Seventy-eight per cent of isolates
TABLE II Infecting Organisms and their Antibiotic Sensitivities. No. sensitive to:
AUGMENTIN No. No. Tested Sensitive
No.
%
38
65.5
19
33
19
24
24
P. Mirabilis
8
13.8
8
3
7
5
5
Strep. spp.
7
12.1
7
6
2
6
6
Klebsiella & other GNB 3
5.2
1
2
1
Staph. saprophyticus
1
1.7
0
0
1
Staph. epidermis
1
1.7
0
1
1
E. coli
TOTALS
58
100
AMP TMP Sulp
35 45 31 (60%) (78%) (53%)
35
35 (100%)
100 Scully et al.
I.J.M.S.
Apra, 1990
test discs and cotton tip swabs cost little. The main expense involved in setting up for DST in a GP practice would be the initial capital outlay on a suitable incubator. This may cost in the region of s The fact that some 43% of MSUs gave equivocal results in the laboratory tests indicates that there are problems in either collection of the specimens or transport of the specimens to the laboratory. If the urinary dipslide technique is not usedz the DST method is a suitable alternative.
Fig. la - Heavy growth of E. coli resistant only to ampicillin and sulphafurazole.
The DST technique is highly sensitive and specific for demonstrating the presence of infection; and for determining antibiotic sensitivities. DST is also easy to perform, rapid and inexpensive. General practitioners should consider this technique as a viable alternative to the practice of sending urine samples to the laboratory. While providing an accurate diagnostic indicator, routine use of DST for the diagnosis of suspected UTI might eliminate such practical difficulties as transport and delay. DST certainly offers the GP more autonomy in the diagnosis and management of a very prevalent condition.
Acknowledgements We would like to thank the following for their help and encouragement: Mr. L. English, Dr. J. B. Walsh, Mr. Eamonn Kiely, Dr. Donal McSorley and Mrs. Mary Foody who typed the manuscript. References
1. McCue, J. D. Urinary tract infection and dysufia, Post Graduate Medicine 1986: 80, 5, 113-142 2. Murphy, D. M., Gillespie, W. A., Cafferkey, M. T.,Nelson, H. G., Falkiner, F. R., Ruddock, G. Urinary tract infection in female patients - a survey in general practice in the Dublin area. Irish Medical Journal 1982: 75, 240242 3. Cafferkey, M. T., Falkiner, F. R., Gillespie, W. A.0 Murphy, D. M. Antibiotics for the prevention of septicaemia in urology. Journal of Antimicrobial Chemotherapy 1982:9.471 477.
Fig. l b - Moderate g r o w t h of sensitive E. coli with intermediate sensitivity to cephradine.
4. Brumfitt, W., Percival A., Williams, J. D. Estimation of bacteria and white cells in urine. Association of Clinical Pathologists Broadsheet 80, 1973.
