Acta Pædiatr 87: 549–52. 1998 Incidence rate of first-time symptomatic urinary tract infection in children under 6 years of age S Mårild and U Jodal Department of Paediatrics, Göteborg University, Göteborg, Sweden Mårild S, Jodal U. Incidence rate of first-time symptomatic urinary tract infection in children under 6 years of age. Acta Pædiatr 1998; 87: 549–52. Stockholm. ISSN 0803–5253 A retrospective population-based study was performed to describe the incidence rate of first time symptomatic urinary tract infection in children under 6 y of age. A total number of 299 children was identified during the 20-month study period in a population of 20 000 girls and 21 000 boys. The cumulative incidence rate during the first 6 y of life was 6.6% for girls and 1.8% for boys. The annual incidence rate in girls of urinary tract infection/1000 at risk was between 9 and 14 for each of the six 1-y age intervals. In girls, the proportion of febrile urinary tract infection was high during the infant year, while girls older than 2 y most often had non-febrile infection. For infant boys, the incidence rate and the proportion of febrile urinary tract infection were comparable to that of girls, while after the first year of life urinary infection of any kind was rare, with an incidence rate of 1–2/1000 at risk. ` Children, incidence rate, urinary tract infection S Mårild, Department of Paediatrics, Sahlgrenska University Hospital East, S-416 85 Göteborg, Sweden In view of the many published studies of urinary tract infection (UTI) in childhood, there are remarkably few that address the epidemiology of this disease. The figures on the incidence rate of UTI most often referred to are those of Winberg et al. (1). In their studies in Göteborg from 1964 to 1966, the frequency of symptomatic UTI during the first 10 y of life was 3.0% in girls and 1.1% in boys. The impression has been that these figures are too low. In 1982, Hellström et al. performed a study of school entrants in the same area. In a questionnaire the parents of all 7-yold school entrants were asked about micturition habits and any previous UTI of their children. The records at the Children’s Hospital or at outpatient clinics were studied to verify any suspected diagnosis of a UTI. The study revealed a cumulative incidence rate of symptomatic UTI of 7.8% in girls and 1.6% in boys during the first 6 y of life (2). We therefore wished to review the data in children with UTI diagnosed during the same time period to see whether these figures could be confirmed using an alternative methodology. Methods With few exceptions sick children received care in the public health care system at the Children’s Hospital and the nine paediatric outpatient clinics of the city (3). General practitioners rarely managed acutely sick infants and small children. Computerized registration of all children with bacteriuria was started at the hospital in 1970. At the time of the study the paediatric outpatient clinics either registered the ICD-8 diagnostic code for all visits, or kept a q Scandinavian University Press 1998. ISSN 0803-5253 special register of patients for whom there was a urine culture. The basis of the study was a survey of children aged ,6 y with first-time febrile UTI performed during 1979–81 at the Children’s Hospital (4). To these children were added all neonates with UTI from the hospital and those with first-time UTI identified at the outpatient clinics during the same period. All the original records of the children with suspected or proven UTI were studied, and the number of children with UTI during each month was determined by the inclusion criteria (see below). The day that antibiotic treatment was started was used to allocate them in time to one of the 20 months studied, and to determine the age of the child. The definitions were used to characterize the infection. The totals for the whole time period were calculated by cumulating the monthly figures. The annual census of the city was used to estimate the total population of children aged between 0 and 6 y. Each year, the exact number of individuals, grouped according to age, sex and residency, was accessible by the first of November. The population in 1-y age groups at the start (A) and the end (B) of the 20 months studied was approximated from the census figures for the period 1 November 1978–1 November 1981. The study population for the assessment of the incidence rate per year and per 1000 at risk was calculated as follows: ðA þ BÞ=2 3 20=12. In addition, the population was corrected by a subtraction of the number of children that had had a UTI, since they were not at risk for a first time infection. The variation in the size of the subpopulations during this time was ,4%. The ethics committee of Göteborg University approved the study. 550 S Mårild and U Jodal Definitions Bacteriuria. Uniform growth of at least 100 000 CFU/ml urine, or any growth in urine obtained by suprapubic aspiration. Febrile or non-febrile UTI. A temperature taken by thermometer was usually available: $38.58C was considered as a febrile and ,38.58C as a non-febrile infection. Exact temperature measurements were missing in 19 outpatients. In these cases, the patient history was used for classification of the infection. Inclusion criteria Children were included if they fulfilled the following criteria: (i) first known episode of UTI; (ii) medical consultation because of symptoms; (iii) antibiotic treatment instituted; (iv) age under 6 y; (v) residents of Göteborg city; and (vi) study period between 15 September 1979 and 16 May 1981 (4). Results The total population of girls at risk was 20 372, varying for ACTA PÆDIATR 87 (1998) each of the 6-y intervals between 3269 and 3705. For boys, the corresponding figures were 21 280, and 3336 and 3877, respectively. A total of 299 children with their first known symptomatic UTI was identified during the study period. Of the 231 girls, 101 were classified as febrile and 130 as non-febrile. The incidence rate of febrile and non-febrile infection per age group for girls is given in Fig. 1. Febrile infection in girls had the highest incidence rate during infancy, 9.7/1000 at risk per year, thereafter slowly declining to a level of 2–5/1000 at risk for 3–6-y-old girls. Nonfebrile UTI was infrequent in female infants; the highest incidence rate, 9.4, was observed during the third year of life, after which the incidence rate was between 7 and 9. The total annual incidence rate for both febrile and non-febrile UTI was between 9 and 14, with the highest incidence during the third year of life. Of the 68 boys, 41 were classified as having febrile infection. The annual incidence rate of febrile UTI in boys was highest during the infant year, 7.7/1000 at risk, after which it declined markedly to a level of ,1/1000 at risk. Non-febrile infection was constantly infrequent among boys, with the peak incidence rate, 2.8, occurring in infant boys. None of the boys was circumcised. During the first year of life the total incidence rate was similar for the sexes, 11.3 and 10.5/1000 at risk for females Fig. 1. The bars indicate the annual incidence rate in 1-y age intervals of febrile and non-febrile urinary tract infection in girls and boys. The figures above each bar represent the actual number of individuals with UTI during 20 months from which the incidence rate was calculated. 551 Incidence rate of urinary infection ACTA PÆDIATR 87 (1998) Table 1. Cumulative number of girls and boys with UTI/1000 at risk before 6 y of age. Cumulative no. with UTI/1000 at risk Reference Country Years studied Total no. with UTI Girls Boys Winberg (1) Brooks (5) Dickinsson (6) McKerrow (7) Uhari (8) Hellström (2) Present study Sweden England England Scotland Finland Sweden Sweden 1964–66 1970–74 1970s 1968–77 1978–84 1975–82 1979–81 342 38 14 572 <5000 177 299 20 66 15 5 27 70 66 7 33 10 2 14 15 18 and males, respectively. There was, however, an unequal sex distribution during the infant year with an accumulation of boys in the early part and of girls in the late part. During the first 2 months of life, 10 boys and 2 girls were identified. Of the total of 299 children, 123 were under 2 y of age and, of these 104 (84%) were diagnosed at the hospital. In comparison, the remaining 176 children aged 2–6 y received their diagnosis in 91 cases (52%) at the hospital. Of the total of 142 febrile infections, 122 (86%) were registered at the hospital. A total of 157 non-febrile infections was recognized, 130 (83%) in girls. Of the 157 non-febrile infections, 84 (53%) were detected and treated at the outpatient clinics. The number of children with UTI per study month was analysed separately. There was a significant decrease with time for the 19 complete months studied (r ¼ 2 0:63, p , 0:01). The decrease was seen only in febrile infection and in girls and did not occur in any specific age group. No seasonal variation was seen. Discussion The results of the present study were similar to those obtained by Hellström et al. (2). To compare results of different studies, we estimated the cumulative number of girls and boys per 1000 at risk with at least one UTI at 6 y of age, using published data on incidence rates (Table 1) (1, 2, 5–8). The variation in the incidence of symptomatic UTI in the studies in Table 1 may have several explanations. Investigations from the 1960s and 1970s are likely to show a lower incidence, since general awareness of UTI was not as high and urine cultures were probably used less frequently. This is illustrated by the studies in Göteborg, which showed considerably lower figures in the 1960s. Part of the variation in incidence may be explained by differences in healthcare traditions and selection of patients. The study by McKerrow et al. (7) with the lowest incidence, is not a true epidemiological study. It only reflects the proportion of children with UTI referred to the hospital for imaging studies. In contrast, Uhari et al. (8) who also studied registers of children hospitalized for UTI, found a higher incidence, possibly indicating a difference in the referral practices of the two different healthcare systems. Studies including patients managed in a primary care setting show the highest incidence rates. The studies by Brooks et al. (5) and Hellström et al. (2) as well as the present one demonstrate similar results. The most important common features are that the highest incidence rates occurred in infants and that girls continued to have first-time infections above 2 y of age, which was seen infrequently in boys. Over the study period, there was a significant decrease in the number of children with UTI and in the incidence rate. The decrease was seen only in females with febrile UTI. The reason for this is not known. It can be speculated that this is part of the normal epidemiological variation seen in community-acquired UTI, which in turn may be associated with variation in medical care, bacterial virulence characteristics or caring and feeding practices. A similar decrease was described by Uhari et al. (9), who made a registry study of all children discharged with a diagnosis of UTI from hospitals in Finland during the period 1978–84. There were several factors in the healthcare system that contributed to a high detection rate of children with UTI in the present study. Children with acute diseases were managed primarily at the Children’s Hospital or the paediatric outpatient clinics. Children suspected of having UTI were traditionally sent to the hospital emergency room for adequate diagnosis and treatment. In addition, all children in Sweden attend Child Health Centres and, particularly in Göteborg, the nurses were well educated as to symptoms and signs of childhood UTI after having participated in previous epidemiological studies (9) . A high incidence rate of childhood UTI is likely to be a reflection of a high detection rate and not a higher incidence of UTI per se. This phenomenon was already noted by Winberg et al. (1) and Littlewood (10), who found that an increased awareness of UTI led to more frequent diagnosis. Detection of UTI, especially in infants, may be of importance to prevent renal insufficiency in young adults, since one of the few preventable causes of renal failure in this age group is sequelae after childhood pyelonephritis. In fact, the high detection rate of UTI and the low frequency of 552 S Mårild and U Jodal end-stage renal disease from reflux nephropathy in Sweden support this assumption (11, 12). Acknowledgments.—The study was supported by the Swedish Medical Research Council, the IngaBritt and Arne Lundberg Foundation and the Frimurar-Barnhusfonden. The statistical advice was provided by Nils-Gunnar Pehrson. References 1. Winberg J, Andersen H, Bergström T, Jakobsson B, Larson H, Lincoln K. Epidemiology of symptomatic urinary tract infection in childhood. Acta Paediatr Scand 1974; 63 Suppl 252: 1–20 2. Hellström A-L, Hanson E, Hansson S, Hjälmås K, Jodal U. Association between urinary symptoms at 7 years old and previous urinary tract infection. Arch Dis Child 1991; 66: 232–4 3. Jodal U. The natural history of bacteriuria in childhood. Infect Dis Clin North Am 1987; 1: 713–29 4. Mårild S, Hellström M, Jodal U, Svanborg Eden C. Fever, bacteriuria and concomitant disease in children with urinary tract infection. Paediatr Infect Dis J 1989; 8: 36–41 ACTA PÆDIATR 87 (1998) 5. Brooks D, Houston I. Symptomatic urinary infection in childhood: presentation during a four-year study in general practice and significance and outcome at seven years. J Roy Coll Gen Pract 1977; 27: 678–83 6. Dickinson JA. Incidence and outcome of symptomatic urinary tract infection in children. BMJ 1979; 1: 1330–2 7. McKerrow W, Davidson-Lamb N, Jones P. Urinary tract infection in children. BMJ 1984; 289: 299–303 8. Uhari M, Nuutinen M. Epidemiology of symptomatic infections of the urinary tract in children. BMJ 1988; 297: 450–2 9. Wettergren B, Jodal U, Jonasson G. Epidemiology of bacteriuria during the first year of life. Acta Paediatr Scand 1985; 74: 925–33 10. Littlewood J. 66 infants with urinary tract infection in the first month of life. Arch Dis Child 1972; 47: 218–26 11. Esbjörner E, Aronson S, Berg U, Jodal U, Linne’ T. Children with chronic renal failure in Sweden 1978–1985. Paediatr Nephrol 1990; 4: 249–52 12. Esbjörner E, Berg U, Hansson S. Epidemiology of chronic renal failure in children: A report from Sweden 1986–1994. Paediatr Nephrol 1997; 11: 438–442 Received Apr. 18, 1997. Accepted in revised form Jan. 2, 1998