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Background: Bacteremia occurs frequently in newborn calves. The predictive value of clinical signs is low, suggesting the use of calf-side diagnostic tests.
Objectives: To investigate testing of urine catalase activity (Uriscreen test) for bacteriuria and bacteremia detection.
Animals: Five colostrum-free calves and 3 colostrum-fed control calves.
Methods: Controlled experimental trial. Colostrum-free calves were inoculated PO with Escherichia coli O78+. A clinical score was established to define the onset of the illness. Blood and urine (cystocentesis) samplings and cultures, and Uriscreen tests, were performed 4–6 times from inoculation to death. Three control calves received the same management as 3 inoculated calves, but with colostrum and without inoculation.
Results: Bacteremia was demonstrated in all of the inoculated colostrum-free calves and in none of the control calves. The E. coli O78+ strain, E. coli, and Klebsiella spp. were recovered from 4/5, 5/5, and 2/5 inoculated colostrum-free calves, respectively. Urine cultures were negative for the 2 groups at the start of the experiment; 5/5 colostrum-deprived inoculated calves were positive for E. coli thereafter whereas 3/3 controls remained negative. Concordance of Uriscreen tests with bacteremia and bacteriuria was 0.86 and 0.88, respectively. Kappa value of agreement between Uriscreen and bacteremia and bacteriuria was 0.73 and 0.76, respectively. Sensitivity of Uriscreen for bacteremia and bacteriuria was 80.0 and 86.6%, respectively, and specificity was 92.8 and 88.8%, respectively.
Conclusions and Clinical Relevance: The results suggest that Uriscreen can be used for detection of bacteremia in neonatal calves in connection with a constant bacteriuria.
Septicemia is common in calves during the 1st days of life.1,2 Bacteremia was demonstrated in approximately 20–30% of diarrheic calves during the neonatal period.1 The bacteria isolated during bacteremia or septicemia include Escherichia coli in >50% of calves, and Salmonella spp., Campylobacter spp., Klebsiella spp., and Staphylococcus spp.2 The rational use of antimicrobial treatment in neonatal calves with systemic illness with or without diarrhea depends largely on the presence or absence of bacteremia.1
The early diagnosis of bacteremia in calves is difficult. Clinical signs and scoring have been proposed, but their predictive value remains low.1–3 Blood culture is considered a definitive test, but time and cost limit its practical use.1 In human infants, septicemia is also difficult to diagnose. Leukogram and C-reactive protein seem to be the most accurate criteria for sepsis diagnosis in humans.4 In 27% (16/59) of human adults with Staphylococcus aureus bacteremia, bacteriuria (>105 CFU/mL) was detected within 48 hours after positive blood culture. Bacteriuria appeared as a consequence of bacteremia in two thirds of cases and as the cause in the other one third.5
Detection of urine catalase activity by the Uriscreen test is commonly used in human emergency clinics as the 1st line of urinary tract infection diagnosis. Catalase activity is present in most bacteria and somatic cells. According to the manufacturer, the Uriscreen test positive threshold is 50,000 CFU/mL of urine,6,7 and moderate specificity (45–80%) and good sensitivity (70–100%) are reported in humans.6–10
The aim of the study reported here was to evaluate the possibility of with the Uriscreen test on urine for the early detection of bacteriuria and indirectly bacteremia in neonatal calves.
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In this study, bacteremia was detected in all 5 inoculated calves and in none of the control calves. Colostrum-free calves are very susceptible to bacteremia after experimental inoculation.2 The pathogenic strain E. coli O78+ was reisolated in blood and organs from 4 of the 5 inoculated calves. However, bacteremia in calf #7 can be attributed only to bacteria considered as opportunistic, E. coli O78− and Klebsiella spp. Those bacteria could have colonized the digestive tract before the experimental inoculation, in accordance with the lack of colostral immune factors in this calf, and as suggested by the early bacteremia detected at inoculation time. These 2 factors may have played a role in the polybacterial infections detected in three of the calves too. The blood cultures demonstrated the presence of bacteremia, which corresponded with postmortem bacterial isolation from liver and kidney.1,2 Finally, bacteremia was present, enabling us to evaluate the Uriscreen test.
The results suggest an association between bacteriuria and bacteremia in all of the calves. In all of the inoculated (bacteremic) calves, urine bacterial counts were positive during the clinical phase and negative before. In all of the control (nonbacteremic) calves, urine bacterial counts remained negative. Moreover, the bacteremia was associated with bacteriuria in all of the calves for E. coli O78− and Klebsiella spp. (4/4 and 2/2, respectively), and in half of the calves (2/4) for E. coli O78+. In human adults with S. aureus bacteremia, the simultaneous detection of S. aureus in urine was shown in only 27% of patients.5
The bacteriuria appeared after bacteremia in all of the calves (Table 1), suggesting a contamination of the urine from the blood. In humans, bacteremia as a consequence of bacteriuria is reported,5 even if bacteremia as a cause seems to be more frequent. Nevertheless, mechanisms leading from bacteremia to bacteriuria are not well understood.5 The formation of microscopic abscesses in the kidney after a blood contamination has been reported.5
Uriscreen tests were positive in 4/5 inoculated calves, but in none of the control calves. Early death and low urine bacterial count could explain the negative result in inoculated calf #8. The false positive results (Table 2) observed in this study cannot be clearly explained. Catalase activity of erythrocytes or of inflammatory cells because of repeated cystocentesis7 probably can be excluded considering the negative peroxidase and leukocyte results on urine samples (data not shown), the lack of macroscopic lesions in the bladder and the negative Uriscreen tests in all of the control calves.
Kappa values between 0.6 and 0.8 are considered to represent good agreement, suggesting value in the use of Uriscreen to detect bacteriuria or bacteremia. Moreover, the sensitivity and the specificity of the Uriscreen test for bacteriuria and bacteremia are close to values reported in humans.6–10 Nevertheless, these evaluations were made on few calves.
Successive samplings in the same calf clearly show that cystocentesis was easy to perform on calves including males and without harmful effects on bladder. In the field, a single cystocentesis can be performed on an ill calf and used for Uriscreen testing. No data are available on the Uriscreen results when voided urine is used instead of samples collected by cystocentesis.
Our results suggest that the calf-side Uriscreen test can be used for the detection of bacteremia in neonatal calves in connection with constant bacteriuria. It would enable reduction in the use of parenteral antibiotics in calves with negative Uriscreen test results.
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a Elanco, Suresnes, France
c Vétoquinol, Lure, France
d Terumo, Leuven, Belgium
e Braun, Melsungen, Germany
f Biomérieux, Marcy l'Etoile, France
g Oxoid, Basingstoke, United Kingdom
h Biovac, Beaucouze, France
i Savyon Diagnostic, Ashdod, Israel