Bacteriuria during indwelling urethral catheterization

Journal

of Hospital

Infection

(1988)

Bacteriuria

during indwelling catheterization

A. B. Mulhall, Nursing

Practice

11, 253-262

R. G. Chapman

Research

Unit,

and R. A. Crow

University

Accepted for publication

urethral

of Surrey,

Guildford

1 June 1987

Summary:

The incidence of bacteriuria and the ritik factors related to its acquisition were determined in a prospective study of 220 hospitalized patients. Bacteriuria was recorded in 971220 (44%) of patients, in 42 cases within 48 h (Group A) and in 55 cases more than 48 h (Group B) after catheterization. The results of a multivariate analysis of Group A demonstrated that the reason for catheterization, the use of antimicrobial chemotherapy and the medical specialty of care were the only variables of those assessed associated with the acquisition of bacteriuria. In a similar analysis of Group B the number of days the catheter was in situ and the use of antimicrobial chemotherapy were the only factors which achieved statistical significance.

words: Bacteriuria;

Key

multivariate

analysis

of bacteriuria;

urinary

catheter

Introduction The presence of an indwelling urethral catheter predisposes to infection of the urinary tract. A recent national survey in the UK reported that 41% of patients suffering from nosocomially acquired bacteriuria were catheterised (Meers et al. 1981). The introduction of ‘closed’ drainage systems has significantly reduced the incidence of catheter associated bacteriuria and septic postoperative complications (Pyrah et al. 1955; Gillespie, 1956). However, the risk of acquiring bacteriuria using modern closed drainage systems has been estimated as 8.1% for each day the catheter remains in situ (Garibaldi et al., 1974). It is postulated that micro-organisms may gain entry to the bladder during the catheterization procedure through contamination of the ‘closed’ drainage system or by migration between the external catheter surface and the urethral epithelium. Although catheter-associated bacteriuria has been widely investigated detailed studies are often confined to relatively specialized populations, e.g. Correspondence University

to: of Surrey,

0195-6701/88/030253

Dr

A. B. Mulhall, Guildford, Surrey

Nursing GU2

Practice SXH.

+ 10 $03.00/O

Research

Unit,

Department

of Biochemistry,

0 1988 The Hospital

253

Infectmn

Society

254

A. B. Mulhall

et al.

spinal injury patients or male genito-urinary patients. Large studies of prevalence, through necessity, cannot include information relating to reasons for catheterization, detailed demographic information about patients, or a description of the catheter system. Similarly retrospective studies such as the Study on the Efficacy of Nosocomial Infection Control (SENIC project) (Hooton et al., 1981) have not accounted for some factors (e.g. catheter care and maintenance) which may affect the incidence of bacteriuria in different patients. As part of a wider investigation of the use of indwelling urethral catheters and related nursing practice (Crow et al., 1986) the incidence of catheter associated bacteriuria was determined in a prospective study of an unselected group of hospitalized patients. Various factors relating to the acquisition of bacteriuria were examined. The results of this part of the study are reported here. Materials

and methods

Patients were recruited during a continuous period of 14 days from 5 District General Hospitals, randomly selected from a sampling frame of 41 District Health Authorities within the south-east of England. All newly catheterized patients (except those under 16 years old, or those in mental handicap, psychiatric and maternity specialities) were included in the study if their catheter remained in situ for longer than 24 h. Patients were studied until their catheter was removed or for a maximum of 21 days. Details of the patient, catheterization procedure and drainage system were recorded. Catheter disconnections were determined by daily checking for misalignment of an indelible mark on the catheter and drainage tube connection. Correct positioning of the drainage bag (i.e., on a stand below the level of the bladder with unobstructed downward flow of urine) was noted daily. Urine for culture was aspirated daily from the catheter tubing, and > lo4 organisms ml-’ isolated on 2 consecutive days was considered significant (Stark & Maki, 1984). Bacteria were enumerated using ‘Dipslides’ (Oxoid Ltd, Basingstoke) and identified using conventional methods (Cowan & Steel, 1977) and API biochemical strips.

Statistical

methods

A multivariate analysis of the relationship between the acquisition of bacteriuria and the following factors was made using a generalized linear model (Nelder & Wedderburn, 1972): sex; age; diagnosis; medical specialty of care; reason for catheterization; person performing the catheterization; place of catheterization; use of antimicrobial chemotherapy; the number of days the catheter was in situ; disconnection of the drainage system; faecal incontinence; presence of another catheterized patient in adjacent bed or same ward and health district. Other associations were explored using non-parametric techniques (Siegel, 1956).

Bacteriuria

and urethral

catheterization

255

Results

Study population 240/1909 patients present in hospital at the start of the survey had an indwelling urethral catheter. During the recruitment period 294 patients were catheterized, representing a daily incidence of 11.2 catheterizations per 1000 of the hospital population. The median age of males was 70 years and of females 67 years, but 27% of females were younger than 50 years compared with 12% of males (Kolmogorov-Smirnov two-sided test. P< 0.025). Fifty-six per cent of patients were admitted for surgery, 28% for investigations and 12% for medical treatment. Half the patients were catheterized on day 1 or day 2 of hospitalization. The catheter was removed from 70% of patients within 7 days (Figure 1).

Acquisition

of bacteriuria Seventy-four patients had their catheter removed before two specimens of urine had been obtained and were therefore excluded from the analysis of factors related to the acquisition of bacteriuria. Bacteriuria was recorded in 97 (44%) of the remaining 220 patients. In 42 of these 97 patients bacteriuria was present by 48 h of catheterization (Group A) and in 55 patients bacteriuria occurred after this time (Group B). For the purposes of the study it was decided that bacteriuria recorded within 48 h may have been derived from either the catheterization procedures or prior Bacteriuria recorded more than 48 h after asymptomatic bacteriuria.

I

2

3

4

5

6

7

8

9

IO

Number

Figure 1. The percentage post catheterization.

of patients

with

II

12

13

14

15

16

17

I8

19 2

of days

the catheter

in

situ against

the

number

of days

A. B. Mulhall

256 Table

et al.

I. Patients included in the analysis of factors associated with the acquisition of bacteriuria (n = 220)

Characteristic

Number No

Total

Bacteriuria by 48 h after catheterization

Bacteriuria more than 48 h after catheterization

62 61

14 28

2’;

67 l&97

71 17-97

47 24 10 11 16

6 4 11 7 :

: 5

5 3

20 7 5 8 4 4 4 3

genito-urinary

36

5

15

56

gastrointestinal

27

2

5

34

skeletal system female system system nervous circulatory

12 18

7 3

9 6

3

6 4

15 13

13 7

11 6

5 5

29 18

123

42

55

Sex Male Female

infection

of patients

103 117

Age

Median Range

Medical specialty Surgical Genito-urinary Medical Orthopaedic Gynaecological Geriatric Neurological Other Primary diagnosis Disorder of the system Disorder of the tract Disorder of the Disorder of the reproductive Disorder of the Disorder of the system Other Not known Total

Table

II.

Multivariate

4 6

5

analysis if risk factors for bacteriuria (Group A)

Factors included in the model

Catheterized for incontinence Catheterized for incontinence + antimicrobial Catheterized for incontinence + antimicrobial therapy + medical speciality Further factors

8-8 15.5 18.5 not

;: 26

220

by 48 h after catheterization

Percentage of variance accounted

therapy

70 1697

; A-91

Significance level for P
PCO.01 significant

(P> 0.05)

Bacteriuria

and urethral

catheterization

257

catheterization was considered to be the result of subsequent infection. Data from these two groups were therefore analysed separately. A basic description of the 220 patients is presented in Table I. In Group A patients the multivariate analysis showed that the reason for catheterization, the use of antimicrobial chemotherapy prior to catheterization and the patient’s medical specialty were the only variables significantly associated with the presence of bacteriuria (Table II). Patients catheterised because of urinary incontinence were 21% (SE 8%) more likely to have bacteriuria than other patients; patients receiving antimicrobial chemotherapy prior to catheterisation were 21% (SE 5%) less likely to have bacteriuria than other patients and patients cared for in surgical, genito-urinary or gynaecological specialties were less likely to have bacteriuria than patients in medical, orthopaedic or neurological specialties (Table II). In Group B patients the incidence of bacteriuria in the study population increased with the number of days the catheter remained in situ, reaching a maximum of 90% in 17 days (Figure 2). The number of days the patient was catheterized and the use of antimicrobial chemotherapy prior to the onset of bacteriuria were the only factors to achieve statistical significance in the multivariate analysis (Table III). The risk of developing bacteriuria, between days 3 and 21, increased by 5% (SE 0.7%) for each day the catheter was in situ and decreased by 23% (SE 6%) with the use of antimicrobial chemotherapy.

80 v) Ea, ; a %

60-

Number

Figure 2. The with a catheter

number in situ.

of patients

of

days

in Group

post-catheterization

B with

bacteriuria

as a percentage

of those

A. B. Mulhall

258 Table

III.

Multivariate

analysis of risk factors for acquiring bacteyiuyia more than 48 h after catheterization (Group B)

Factors included in the model

Number Number Further

Infecting

of days of days factors

et al.

Percentage of variance accounted catheterized catheterized

+ antimicrobial

therapy

Significance level for

24.1 29.5 Not significant

PC 0.001 PC 0.001 (P > 0.05)

organisms

One hundred and twenty-three organisms were isolated from 97 patients. In 73 patients a single organism was isolated and in the remaining 24 two or more organisms were cultured. There was an even distribution of gram-negative (48%) and gram-positive (45%) bacteria. Escherichia coli was the most common infecting organism (22%), while other enterobacteria accounted for 26% of isolations. Staphylococcus aureus and S. epidermidis were each cultured from 12% of infected urines. Staphylococcus epidermidis was cultured more frequently from males (Chi-square= 6.9, d.f. = 1, PC 0.01) while E. coli was more frequently isolated from females (Chi-square = 7.0, d.f. = 1, P< O-01). Other organisms were more evenly distributed between the sexes. There were no significant differences in infecting organisms between different districts. No associations between age and infection with particular organisms were identified but the numbers involved were small and the statistical power was weak. However, infections caused by Streptococcus faecalis or by Proteus spp. were recorded only in patients over the age of 50 years. Further statistical analysis of other factors (e.g. medical specialty of care) would have been invalid due to the small sample sizes. Discussion

The prevalence of indwelling urethral catheters in this study (12.6%) is similar to that reported in the European multicentre prevalence study (Jepsen et al., 1982). From the daily incidence of new catheterizations (11.2 per 1000 patients) it may be estimated that approximately 2000 patients (95% confidence interval 1500 to 2500) in a SOO-bed District General Hospital may be catheterized during a year. Thus a large population is at risk of acquiring catheter related nosocomial UTI. The high incidence of bacteriuria at 2 days post-catheterization recorded in this study (31%) compares unfavourably with the 14% reported by Burke in the USA (Burke, Larsen & Stevens, 1986), but is similar to figures reported by Shapiro et al. (1984). Whether the low incidence reported by Burke is a reflection of a younger, healthier study population or improved nursing practice or both is not clear.

Bacteriuria

and urethral

catheterization

259

The incidence of catheter-related bacteriuria may be influenced by a variety of factors, but two main categories may be identified: host determined factors (e.g., age, sex, underlying illness) and hospital determined factors (e.g. surgical procedures, chemotherapy, length of hospital stay). Univariate analysis has often been used to define risk factors contributing to catheter related bacteriuria (Kunin & McCormack, 1966; Garibaldi et al., 1974; Warren et al., 1978). However, there are often close inter-relationships between putative risk factors and as shown by our analysis and those of Hooton et al. (1981) and of Shapiro et al. (1984) multivariate analysis may be more appropriate. Bacteriuria within 48 h of catheterization was recorded in a large proportion (42/220) of the patients in this study. There is little information available in the literature concerning early onset of bacteriuria in catheterized patients. From the data collected it was not possible to determine in how many patients bacteriuria was present before or occurred during the catheterization procedure. However, the analysis indicated that patients most at risk of having bacteriuria by 48 h after catheterization are those catheterized for incontinence; those who do not receive antibiotics and those being cared for in medical, orthopaedic or neurological specialities. Bacteriuria acquired more than 48 h after catheterization was probably derived either from migration of the peri-urethral flora into the bladder or by contamination of the drainage system by poor nursing practice. The number of days the catheter remains in situ is clearly the overwhelming risk factor, of those assessed, accounting for 24% of the variation in the multivariate analysis. This agrees with both the findings of the retrospective SENIC project (Hooton et al., 1981) and the prospective study of Shapiro et al. (1984). Other studies (Garibaldi et al., 1974) have reported that female sex, advanced age and severity of underlying illness are associated with an increased incidence of catheter-associated bacteriuria. In our study neither sex nor age were independently associated with the risk of acquiring bacteriuria, concurring with the results of the multivariate analysis of Shapiro et al., (1984). Several investigators have documented a relationship between breaks in the closed drainage system and an increased incidence of urinary infection (Platt et al., 1983, Shapiro et al., 1984). However, in agreement with Burke et al. (1986), we were unable to confirm this in our study. It is necessary to further clarify the source of infection in these patients before a rational analysis is possible because, if the majority of are derived from transurethral spread of organisms, infections disconnections of the drainage system will have little effect on the incidence of bladder bacteriuria. There is controversy concerning the source of infecting organisms in catheter associated bacteriuria. Drainage bag contamination has been reported in 17-53% of patients with bladder bacteriuria (Thornton & Andriole, 1970; Brehmer & Madsen, 1972; Maizels & Schaeffer, 1980). However, the temporal relationship between infection in the bladder and

260

A. B. Mu&all

et al.

that in the bag is important since bacteria in the bladder (from whatever source) will quickly descend into the bag. Kunin & McCormack (1966) observed simultaneous infection of the bladder and drainage bag urine and suggested therefore that the bladder was the source of bacteria. Similarly Gillespie et al. (1983) never observed infection of the bag urine before infection of the catheter tube urine and Brehmer & Madsen (1972) never isolated the same bacteria from bag tap outlets and catheter tube urine. In contrast, contamination of the urine bag preceded urinary infection in 17/23 patients studied by Thornton 8z Andriole (1970). It is clear from our own studies, those of Hooton et al. (1981) and Shapiro et al. (1984), that several variables may influence the incidence of bacteriuria in different groups of patients. The influence of these variables must be considered when investigating the routes of infection in patients with bladder bacteriuria. There is surprisingly little detailed information relating to the aetiology of nosocomial catheter related bacteriuria. Most reports have considered only one specific population, e.g., spinal cord injury and renal transplant patients (Schaeffer 8z Chmiel, 1983) or male urological patients (Bultitude & Eykyn, 1973: Gillespie et al., 1983). Fowler (1983) states that the majority of catheter associated urinary-tract infections are caused by Gram-negative bacilli or enterococci. In our study 48% of infections were caused by gram-negative bacilli and 15 % by Streptococcus fuecalis. No association between age and type of infecting organism was established in the present study due to the small numbers involved. However, infections caused by S. faecalis and Proteus spp. were recorded only in patients over 50 years old. This possible association needs clarification in a larger study. Some pertinent facts should be emphasized in the present study. Firstly, some 2500 patients in an average sized District General Hospital in the UK may be catheterized during a 1a-month period. Almost half of these patients may acquire bacteriuria and be at risk of further septic complications. Catheters should be removed as soon as possible since their presence as a ‘foreign body’ is the major risk factor for acquisition of bacteriuria. Other risk factors associated with an increased rate of bacteriuria e.g., catheterization for obstruction or incontinence require further investigation. To improve clinical practice it is essential that the reasons for the relatively high rate of bacteriuria recorded in the present study are fully elucidated. It is clear from the study that certain groups of patients are inherently more at risk for acquiring bacteriuria and may require special preventative measures. However, in our analysis only 18.5% (Group A) and 29.5% (Group B) of the total variation associated with the risk of acquiring bacteriuria was accounted for. The relatively small number of patients in some subgroups clearly influences the statistical power of the analysis and may well explain why some factors failed to achieve statistical significance. Further studies with more selected and accurately defined populations need

Bacteriuria

and urethral

to be conducted to determine acquiring bacteriuria.

what

catheterization

other

variables

261

affect

the risk of

This study was funded by the Department of Health and Social Security. We gratefully acknowledge those hospitals who participated in the survey and the microbiologists concerned for allowing us to use their facilities for our laboratory work. The authors gratefully acknowledge the contribution to the study of MS B. H. Roe and Mrs J. A. Wilson.

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