Dipstick Screening for Urinary Tract Infection in

Febrile Infants

Journal Club

Tuesday 15th July 2014

Charlotte Elder

Background

• SBI occurs in 10-15% 1-90 day olds

• UTI commonest cause SBI

• Utah– Neonates – FSS and empirical Abx

– >28/7 – screen tests and ? admit

• NICE – Infants <3/12 – urine testing

– Urgent M+C for infants <3/12

– Dipstick for children >3yrs

SCH guideline (7.1)

“Children younger than 2 years of age:

– Urgent microscopy and culture preferred method for diagnosing UTI

– Dipstick analysis may be unreliable”

• Nitrites– Urinary micro-organisms reduce nitrate to nitrite– Nitrate needs to be in contact with bacteria for “some time”– Not all bacteria – Too quick in under 2s?

• Leucocytes (LE)– LE enzyme contained in WBC– UTI not the only cause of pyuria

• Evidence base?

Systematic review

• 6 studies

• Dipstick signif less good in < 2yrs

• LR

– +LR 38.5 vs 7.6

– -LR 0.13 vs 0.34

Mori et al. Acta paediatrica 2010;99:581-584

The Clinical Question

Population Children less than 2 years with suspected UTI

Intervention Dipstick urine testing or urine microscopy

Comparison Urine culture

Outcome Accurate diagnosis of UTI

Aim

Comparing performance of urine dipstick alone with

urine microscopy and with both tests combined as

a screen for UTI in febrile infants aged 1 - 90 days.

Methods

• Retrospective observational study

• July 2004 – December 2011 (7.5 yrs)

• Multi-centre (23 hospitals)

• Same diagnostic equipment and database

• Patients identified from database

– Febrile infants and age

– Reason for visit

– Admitting diagnosis

– ICD-9 and coding

Methods

• Age 1-90 days

• Catheterised urine – 10mls

– Dipstick

– Microscopy of centrifuged urine

– Culture

• Medical records r/v if UTI but dipstick negative for

outcome (29-90 days)

Definitions - cultures• Positive for UTI

– ≥1 pathogen

– ≥50,000 CFU/ml (half the “classic” definition)

• Negative for UTI– No bacterial growth

– Growth of contaminant only

• <105 CFU/ml common skin GU flora

– Multiple bacteria each <105 CFU/ml

• Equivocal– Urine pathogens 10,000-49,000 CFU/ml

– Excluded from analysis

Definitions – dip/micro/combo

• Positive for UTI - dipstick

– LE positive

– Nitrite positive

– ≥ trace

• Positive for UTI - microscopy

– >10 WBC per hpf

– ≥ 1 bacteria per hpf

• Positive UTI – combined

– Positive dipstick OR

– Positive microscopy

Results

Study flow chart

Results

6394 febrile infants

770 UTI (12%) 5624 no UTI

1745 (27%)neonates

4649 (73%)29-90 days old

6394 febrile infants

p = <0.001

Sensitivity = true positives

p = <0.001

Specificity = true negatives

p = <0.001

p = <0.001

p = <0.001

p = <0.001

Example

• Prevalence in 29-90 day old infants = 11.9%

• 1000 febrile infants

– 119 culture positive UTI

– Dipstick alone

• 90.4% true positive pick up (108/119) – 9.6% false negative

• 6.2% false positive rate (55 of 881)

– Combined urinalysis

• 94.8% true positive pick up (113/119) – 5.2% false negative

• 10.9% false positive rate (96 of 881)

• 8 treated who don’t have UTI for every 1 infant missed

Critical appraisal

• Does the study address a clearly focused question?

• Did the study use valid methods to address the Qu?

• Are the valid results of the study important?

• Are the valid, important results applicable to our local

population?

• Were all clinically important outcomes considered?

• Are the benefits worth the harms/risks/costs?

Summary and Conclusion

Good to rule out UTI

CLINICAL BOTTOM LINE

Can dip infants’ urine?