Strengths and limitations of study
respiratory tract infection
RESPIRATORY TRACT INFECTION, RECRUITMENT
Strengths of the study include widespread geographical recruitment of general practices, rigorous study design and conduct, and near 100% completeness for the primary outcome. Using different recruitment strategies,Limitations of the study include that the March 2020 and subsequent covid-19 lockdowns meant a wholesale change from face-to-face to remote consultations in primary care, as well as greatly reduced capacity to support non-covid research. The CHICO intervention was designed for use in face-to-face consultations, and clinicians may have been reluctant to use it remotely. Secondly, recorded intervention use was low in relation to the likely number of 0-9 year old children in whom it could have been used; interviews with clinicians suggested that they often used the tool for “borderline” cases, and usage also dramatically fell after March 2020. We estimated use assuming that the dispensed items were all for respiratory tract infection consultations and that 50% of the children consulting were given these. The dispensing rate in the intervention arm was 15.5 items per 100 children; given that the median number of 0-9 year olds was 975 children in 144 intervention practices, this yields 21 762 dispensed items and 43 524 consultations for respiratory tract infection. This is speculative but would suggest that the 11 944 uses of the intervention was around one in every four consultations. This could have been higher if clinicians were able to determine prognostic risk group by memory. Thirdly, less than half of the eligible CCGs approached took part in the study; the difficulty in contacting some CCGs or lack of response makes assessing what bias this may have introduced difficult, although we did have at least one CCG in each of the 15 clinical research network areas in England. Fourthly, just over a quarter of the practices that expressed an interest and met the eligibility criteria subsequently declined, citing lack of capacity or failing to return forms. The impact of the pandemic may have played a part, but this questions the generalisability of the findings. Fifthly, around 2.5% of practices close or merge each year in England, and the number of multiple site practices was larger than anticipated (28%), substantially increasing the number of registered patients. which has implications for cluster trials and sample size calculations. The contrast in antibiotic dispensing rates between arms in multiple site practices compared with single site practices was notable and questions whether a single practice champion for multiple sites was able to promote intervention use effectively. Sixthly, a further limitation was use of the number of children aged 0-9 registered at the practice as the denominator rather than the number of children consulting for respiratory tract infection. A detailed record of how many children consulted for respiratory tract infection and whether the intervention was used would have been difficult to obtain, but its absence limits our ability to comment on whether the intervention was used as planned or whether a lack of use affected our findings. Finally, general advice is that algorithms should be externally validated before an evaluation of clinical effectiveness. However, this was not possible given the absence of a suitable dataset.