Children with urinary tract infection often have anatomical or functional abnormalities in their urinary tract. Imaging studies are therefore recommended, especially for young children, after the first urinary tract infection.1–3 There is, however, considerable variation in clinical practice and some resistance to diagnostic imaging for childhood urinary tract infection.4 We conducted this study to find out whether an association exists between the bacterial species causing the first urinary tract infection and abnormal findings in subsequent imaging studies.
Patients, methods, and results
We examined retrospectively the hospital records of all children with a positive urine culture from a sample obtained by suprapubic aspiration (any growth) or catheterisation (growth of at least 103 colony forming units/ml) during January 1980 to December 1994. Asymptomatic children and those who had been in hospital for more than 2 days before the specimen was obtained were excluded. Children with proved infection had intravenous pyelography (1980-3) or ultrasonography (1984-94) plus voiding cystourethrography (radiographic in boys and nuclear in girls) 1-2 months after the acute infection.
We identified 1237 positive urine samples. Of these, 942 (76%) were obtained by suprapubic aspiration and 295 (24%) by bladder catheterisation. There were 982 (79%) cultures positive for Escherichia coli, 66 (5.3%) for Enterococcus sp, 55 (4.4%) for Klebsiella sp, 47 (3.8%) for coagulase negative staphylococcus, 39 (3.2%) for Proteus sp, and 48 for other species. Of the 207 patients with enterococcal, klebsiella, coagulase negative staphylococcal, or proteus infections, hospital records were available for 201. Forty one patients were excluded (20 had asymptomatic bacteruria, seven had chronic urinary problems such as neurogenic bladder, and in 14 cases one or both of the urinary tract imaging studies were lacking). The urinary tract infection was the first in 92 of the remaining 160 children with infections other than E coli.
We compared the results of these children with those of 92 age and sex matched children whose first urinary tract infection was caused by E coli. Student’s t test was used to compare the mean serum C reactive protein values in the two groups. The frequency of abnormalities in the urinary tract was compared by Pearson’s χ2 test or Fisher’s exact test if the number of expected observations was five or less in at least one cell.
The table shows the characteristics of the 184 patients and findings in the imaging studies. There were significantly more abnormalities among children with enterococcal, klebsiella, or coagulase negative staphylococcal infections than in children infected with E coli. The rate of corrective surgical procedures was also substantially higher in these patients. Only two abnormalities were diagnosed in children with proteus infection.
Comment
Our results agree with earlier studies showing that about 80% of urinary tract infections are caused by E coli and that vesicoureteral reflux is found in about a third of children with infections caused by E coli.3 We also found that when the first infection was caused by klebsiella or enterococcus the rate of vesicoureteral reflux was almost double and that surgical procedures were four times more common in children with infections caused by these organisms than in those with infections caused by E coli.
E coli lacking putative virulence factors such as gal-gal specific adhesins are overrepresented in patients with pyelonephritis associated with vesicoureteral reflux.3,5 Similarly, in children with acute pyelonephritis, renal scarring is significantly more common in those infected with non-E coli organisms3 and with E coli strains that do not possess certain virulence determinants.5 The bacteria probably do not need special virulence properties if the host has an abnormality such as vesicoureteral reflux.
Table.
Age, sex, imaging results, and operations in children according to cause of first urinary tract infection. Values are numbers (percentages) unless stated otherwise
| E coli | Proteus | Klebsiella | Enterococcus | Coagulase negative staphylococcus | |
|---|---|---|---|---|---|
| No of patients | 92 | 26 | 26 | 26 | 14 |
| Age <2 years (boys/girls) | 39/19 | 12/2 | 12/7 | 11/8 | 4/2 |
| Aged ⩾2 years (boys/girls) | 17/17 | 7/5 | 3/4 | 6/1 | 1/7 |
| Mean (SD) C reactive protein (mg/l) | 69 (47) (n=74) | 23 (24)*** (n=16) | 83 (62) (n=16) | 88 (66) (n=23) | 39 (53) (n=9) |
| Reflux | 30 (33) | 2 (8)* | 16 (62)** | 16 (62)** | 5 (36) |
| Grade 1-3 | 26 | 1** | 9 | 9 | 3 |
| Grade 4-5 | 4 | 1 | 7** | 7** | 2 |
| Obstruction | 1 (1) | 0 | 4 (15)** | 3 (12)* | 2 (14)* |
| Other anatomical abnormalities† | 4 (4) | 0 | 2 (8) | 0 | 1 (7) |
| Children with abnormalities‡ | 32 (35) | 2 (8)** | 18 (69)** | 17 (65)** | 6 (43) |
| Operation or injection therapy for reflux | 7 (8) | 2 (8) | 10 (38)*** | 12 (46)*** | 5 (36)** |
P<0.05, **P<0.01, ***P<0.001 compared with E coli infections.
These patients had ureter duplex, except patient with staphylococcus who had a polycystic kidney.
Some patients had both vesicoureteral reflux and other anatomical abnormalities.
Footnotes
Funding: Paediatric Research Foundation and Academy of Finland.
Competing interests: None declared.
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