Changing policy to treat foals with Rhodococcus equi pneumonia in the later course of disease decreases antimicrobial usage without increasing mortality rate
Arnold‐Lehna, D. et al. (2020) Changing policy to treat foals with Rhodococcus equi pneumonia in the later course of disease decreases antimicrobial usage without increasing mortality rate. Equine Veterinary Journal, 52, pp. 531– 537
The objective of this retrospective study was to determine whether targeted treatment of foals with R equi resulted in a decrease in antimicrobial usage without increasing mortality rate.
The study used data from a German breeding farm with a history of foal pneumonia related to R equi, collected during 2008-2016. Foals of 21 days or older with an abscess score ≥ 1cm were eligible for inclusion. All foals born in the nine-year study period that met the inclusion criteria were entered into a spreadsheet, and then for each year, 330 foals were randomly selected. After excluding foals with incomplete data, or those involved in previous treatment studies, there was a total study enrolment of 2,756 foals. The farm health monitoring programme included weekly physical examination from birth to weaning, from which a variety of variables were recorded and a clinical score calculated. In addition, sonographic examination of foals older than three weeks with signs of respiratory disease took place. As part of the programme, the diameters of abscesses were added together to give an abscess score measured in cms.
Before 2012, the farm’s treatment protocol required the presence of severe clinical signs and an abscess score exceeding 1 cm in diameter. From 2012 to 2016, the minimum abscess score required to initiate treatment increased incrementally from >8 cm, in 2012, to >15cm, in 2016. Foals with an abscess score smaller than the minimum received close monitoring and no treatment. Foals with a higher than minimum abscess score received the necessary antimicrobial treatment for six weeks. If pulmonary lesions were still detectable after this period, the foals received a further two weeks of antimicrobial treatment. In both periods, foals with mild to moderate pneumonia were treated with rifampin and tulathromycin, and foals with more severe pneumonia were treated with rifampin and azithromycin.
Analysis was carried out by grouping the foals into two time periods – 2008-2011 and 2012-2016. Results showed that the median abscess score at the beginning of therapy increased significantly from 4cm in 2008-2011 to 11.5 cm in 2012-2016.
The percentage of foals treated with antimicrobials decreased significantly from 81.9% (2008-2011) to 50.9% (2012-2016) and the treatment failure rate decreased significantly from 20.3% to 5.9%. Recurrence after treatment also decreased significantly from 20.6% to 11.6%. The percentage of foals that died from pneumonia or R equi infection did not differ significantly in the two periods.
Limitations include the retrospective nature of the study, with a lack of clarity over some of the collected data and that the data was from a single farm.
This study provides some evidence that selective treatment of foals with pneumonia due to R equi, based on an assessment of abscess score, can decrease antimicrobial usage without increasing the mortality rate. Starting treatment in foals when there was a higher abscess score did not cause either an increased treatment failure or recurrence rate.
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