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Background: Since changes in the national guidance in 2011, prophylactic antibiotics for women undergoing caesarean section are recommended prior to skin incision, rather than after the baby’s umbilical cord has been clamped. Evidence from randomised controlled trials conducted outside the UK has shown that this reduces maternal infectious morbidity; however, the prophylactic antibiotics also cross the placenta, meaning that babies are exposed to them around the time of birth. Antibiotics are known to affect the gut microbiota of the babies, but the long-term effects of exposure to high-dose broad-spectrum antibiotics around the time of birth on allergy and immune-related diseases are unknown. Objectives: We aimed to examine whether or not in-utero exposure to antibiotics immediately prior to birth compared with no pre-incisional antibiotic exposure increases the risk of (1) asthma and (2) eczema in children born by caesarean section. Design: This was a controlled interrupted time series study. Setting: The study took place in primary and secondary care. Participants: Children born in the UK during 2006–18 delivered by caesarean section were compared with a control cohort delivered vaginally. Interventions: In-utero exposure to antibiotics immediately prior to birth. Main outcome measures: Asthma and eczema in children in the first 5 years of life. Additional secondary outcomes, including other allergy-related conditions, autoimmune diseases, infections, other immune system-related diseases and neurodevelopmental conditions, were also assessed. Data sources: The Health Improvement Network (THIN) and the Clinical Practice Research Datalink (CPRD) primary care databases and the Hospital Episode Statistics (HES) database. Previously published linkage strategies were adapted to link anonymised data on mothers and babies in these databases. Duplicate practices contributing to both THIN and the CPRD databases were removed to create a THIN–CPRD data set. Results: In the THIN–CPRD and HES data sets, records of 515,945 and 3,945,351 mother–baby pairs were analysed, respectively. The risk of asthma was not significantly higher in children born by caesarean section exposed to pre-incision antibiotics than in children whose mothers received post-cord clamping antibiotics, with an incidence rate ratio of 0.91 (95% confidence interval 0.78 to 1.05) for diagnosis of asthma in primary care and an incidence rate ratio of 1.05 (95% confidence interval 0.99 to 1.11) for asthma resulting in a hospital admission. We also did not find an increased risk of eczema, with an incidence rate ratio of 0.98 (95% confidence interval 0.94 to1.03) and an incidence rate ratio of 0.96 (95% confidence interval 0.71 to 1.29) for diagnosis in primary care and hospital admissions, respectively. Limitations: It was not possible to ascertain the exposure to pre-incision antibiotics at an individual level. The maximum follow-up of children was 5 years. Conclusions: There was no evidence that the policy change from post-cord clamping to pre-incision prophylactic antibiotics for caesarean sections during 2006–18 had an impact on the incidence of asthma and eczema in early childhood in the UK. Future work: There is a need for further research to investigate if pre-incision antibiotics have any impact on developing asthma and other allergy and immune-related conditions in older children. Study registration: This study is registered as researchregistry3736. Funding: This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 30. See the NIHR Journals Library website for further project information.

Objectives To assess the accuracy and completeness of information provided by websites selling home self-sampling and testing kits for COVID-19.Design Cross-sectional observational study.Setting All websites (n=27) selling direct to user home self-sampling and testing kits for COVID-19 (41 tests) in the UK (39 tests) and USA (two tests) identified by a website search on 23 May 2020.Main outcome measures Thirteen predefined basic information items to communicate to a user, including who should be tested, when and how testing should be done, test accuracy, and interpretation of results.Results Many websites did not provide the name or manufacturer of the test (32/41; 78%), when to use the test (10/41; 24%), test accuracy (12/41; 29%), and how to interpret results (21/41; 51%). Sensitivity and specificity were the most commonly reported test accuracy measures (either reported for 27/41 [66%] tests): we could only link these figures to manufacturers’ documents or publications for four (10%) tests. Predictive values, most relevant to users, were rarely reported (five [12%] tests reported positive predictive values). For molecular virus tests, 9/23 (39%) websites explained that test positives should self-isolate, and 8/23 (35%) explained that test negatives may still have the disease. For antibody tests, 12/18 (67%) websites explained that testing positive does not necessarily infer immunity from future infection. Seven (39%) websites selling antibody tests claimed the test had a CE mark, when they were for a different intended use (venous blood rather than finger-prick samples).Conclusions At the point of online purchase of home self-sampling COVID-19 tests, users in the UK are provided with incomplete, and, in some cases, misleading information on test accuracy, intended use, and test interpretation. Best practice guidance for communication about tests to the public should be developed and enforced for online sales of COVID-19 tests.