Research, published in the journal Anaesthesia, looked at the presence of COVID-19 antibodies in staff from two London hospital maternity units.
Prof Sebastian Johnston, Professor of Respiratory Medicine & Allergy, Imperial College London, said:
“This is an interesting study with several interesting findings.
“They tested healthcare workers who had no current symptoms of COVID-19 at the time of testing and who had not previously had a swab positive SARS-CoV-2 infection. They used the Abbott test, which claims 100% sensitivity based on validation in only 31 severe hospitalised cases, which are likely to have had extremely high antibody levels. The Abbott test (and other tests that have not been validated in milder community cases of COVID-19 or in asymptomatic cases) therefore likely considerably underestimates antibody positivity in milder community COVID-19 cases and in asymptomatic infections. The overall positivity rate of 14.5% is therefore likely a considerable underestimate of true positivity, due to the likely high, but currently unknown false negative detection rate in milder cases with the Abbott antibody test, and because those with previous swab positive infections were excluded from the study.
“Another interesting finding was the high rate of asymptomatic infections, as 35.5% of people who did test antibody positive reported no symptoms at all. It is likely that an even greater proportion of cases with false negative antibody tests would have been asymptomatic. These data are consistent with other reports, such as the REACH2 data reporting that 70% of swab positive cases reported no symptoms in the week preceding their positive swab, indicating that SARS-CoV-2 infection is likely to have been very much more widespread than currently estimated.
“Finally the study reports that 59% of people who did test antibody positive did not self-isolate at any point and continued to work in the hospital setting. Again it is likely that a substantial number of workers with false negative antibody tests would have also continued working, despite being infected. The potential for such large numbers of people, who continued working despite being infected, to further spread the virus to their co-workers and their patients, is obvious.
“These data together are very consistent with an increasing body of work indicating that SARS-CoV-2 infection in the UK is likely to have been very much more widespread than currently estimated. The implication is that any second wave that may occur in the UK, is likely to be very much smaller than current estimates suggest.”
Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:
“During 11 May to 5 June 2020, the study recruited 200 adult, patient-facing maternity workers who had never been positive in a swab-test (Have I got it) from the maternity units of two central London teaching hospitals: 29/200 had IgG antibodies to SARS-Cov-2 and 10 out of these 29 (34%; 95% CI: 16% to 63%) had experienced no symptoms.
“This study underscores the importance of learning efficiently about asymptomatic infection in high-risk settings – such as in persons quarantined by Test & Trace. Reforms announced this week to Test & Trace address the failure to trace. Whether key recommendations by the Royal Statistical Society on learning cost-effectively about asymptomatic infections and adherence to “stay home” will also be heeded remains unclear but I sincerely hope so – for all our sakes.
“Participation-rate by those invited to take part in the maternity worker surveillance is not reported, which is remiss; or I’ve missed it.
“Likewise, it is unclear whether correction was made for sensitivity and specificity of the IgG antibody test selected (Abbott Laboratories 2-step chemiluminescent micro-particle immunoassay technology, for which independently validated 95% confidence intervals for sensitivity and specificity were not cited).”
Dr Edward Morris, President of The Royal College of Obstetricians and Gynaecologists, said:
“This study adds to the evidence that has already been gathered on antibody testing to show that some healthcare professionals, and many members of the general population, have had COVID-19 without knowing it, or having had any symptoms. This research serves to highlight the importance of following COVID-19 policies to limit the spread of the disease, including regular handwashing, social distancing where possible, wearing masks and other PPE and the offer of regular testing to all healthcare staff, including those who are asymptomatic. Rates of infection are generally low and, as noted in the College guidance on COVID-19 infection and pregnancy, it is essential for pregnant women to continue to attend for antenatal care throughout their pregnancies.”
Prof Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases, University of Nottingham, said:
“There is increasing recognition that COVID-19 may be mild or asymptomatic. Anosmia was only recognised as a key symptom later in the pandemic when cough and high fever were originally thought to be the key features. Our understanding of COVID-19 has improved over the past few months.
“Interestingly the rate of positive tests for COVID-19 antibodies in front line workers is similar to the local blood donor population suggests that transmission may not have always occurred as a result of front line working and suggests PPE is effective in stopping some COVID-19 infections although there is no mention in the paper about what PPE was being used by staff during the period of study.
“Asymptomatic health care workers with COVID-19 pose a risk of spreading the virus depending on the PPE in use. We know many cases were acquired in hospital.
“Regular testing of health care workers is clearly warranted.”
Prof. Tim Spector, Professor of Genetic Epidemiology, King’s College London:
“This observational study of maternity staff confirms the high rates of infection in hospital workers, many of whom were apparently asymptomatic. The limited list of official symptoms meant that half the cases were missed and did not self-isolate and so increased infection rates in hospitals. Although other UK studies are showing lower asymptomatic rates when subjects are more closely questioned, this paper is a useful reminder of the importance of educating medical staff on the full range of symptoms of Covid-19, especially before the second wave hits the UK.”
‘A cross-sectional study of immune seroconversion to SARS-CoV-2 in frontline maternity health professionals’ by Bampoe et al was published in Anaesthesia at 23:01 UK time on Tuesday 11 August 2020.
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