A rather beautiful review and meta-analysis by colleagues at Imperial College London examines the evidence around the secondary attack rate (SAR) for SARS-CoV-2 in various settings, highlighting the risk of prolonged contact in homes as the highest risk for transmission.Continue reading
During the first wave of COVID-19, we developed a ‘PPE Helper’ programme. This ward-based programme put PPE experts on the front line to spend time with staff to improve PPE knowledge, promote safe and effective use, and address staff anxiety. The programme was evaluated through a survey of staff views about PPE at the conclusion of the programme. This found that staff who had had contact with a PPE helper responded more positivity to questions about PPE and felt less PPE-related anxiety too.Continue reading
If you’ve had to self-isolate for 14 days following a possible exposure to somebody with COVID-19, you’ll relate to just how long it feels. Towards the start of the pandemic, the Otter family entered a 14 day household self-isolation due to COVID-like symptoms in the pups. At that time, mass testing was not available and so we’re left hanging to this day as to where or not it was or wasn’t. But where does the 14 days come from? And how does the probability of developing COVID-19 following exposure change over time? I was asked this yesterday, and came across a very hand review and meta-analysis of studies related to the SARS-CoV-2 incubation period.
The review includes, published in BMJ Open, includes nine studies in the meta-analysis. Overall, the median incubation period was 5.1 days, and the 95% percentile was 11.7 days (see the Figure below). The team recognise that things will change as new studies come along, so helpfully have published an R Shiny app that will be updated as new data is published. Quite a clever trick, although the Shiny app isn’t the most intuitive.
In answer to your specific question about the difference in risk on day 10 vs. day 14 following exposure, this is tricky and will depend on a number of factors. However, the risk of developing COVID from the point of exposure changes over the 14 days peaking around day 4/5. I’ve attached a systematic review and meta-analysis of the COVID incubation period. Figure 5 is probably most helpful, which shows from the meta-analysis of 8 studies that approx. 90% of individuals who would eventually test positive had tested positive by day 10, whereas >95% had tested positive by day 14.
International guidelines recommend an isolation period of 14 days following patient or staff exposure to COVID-19 (see PHE and CDC). So why 14 days? And not 13 or 16? As you can see, the odd person developed COVID-19 outside of the 14 day window since exposure, but this is uncommon. And I think there’s something pragmatic about 14 days being 2 weeks!
The issue of preventing healthcare-associated COVID-19 is very topical right now, to say the least (see this JAMA commentary), so now is a really good time to review what happened in our hospitals during the ‘first wave’ to help us prevent hospital transmission during the second.
The study was performed during the first wave of COVID-19 in London, between March and mid-April. The focus of the study was on ‘hospital-onset definite healthcare-associated’ (HODHA) COVID-19 infections (with a sample date >14 days from the day of admission). Overall, 58 (7.1%) of 775 symptomatic COVID-19 infections in hospitalised patients were HODHA. Key findings included:
- Compared with community-associated COVID-19, patients with HODHA were more likely to be older, Black Asian or Minority Ethnicity (BAME), have several clinical underlying conditions (e.g. malignancy), and had an increased length of stay after COVID-19 diagnosis. Surprisingly, there was no increased risk of mortality (either 7, 14, or 30-day) or ICU admission.
- There was an interesting analysis of the impact of a delayed positive test (where there was no positive test within 48 hours of symptom development). This occurred in about a third of HODHA cases, and was associated with an increased risk of 30-day mortality.
- A potential source patient (a positive case on the same ward within 14 days of the positive test) was identified for 44/58 HODHA cases.
- There was a correlation between weekly self-reported sickness absence incidence and weekly HODHA incidence.
This is a similar piece of work to our analysis of healthcare-associated COVID-19. The period of time covered was almost identical (from March to mid-April) and the number of HODHAs was very similar (62 in our study compared with 58 in this study). This seems to illustrate how indiscriminate this outbreak has been regionally – a wave of healthcare-associated COVID-19 swept through our hospitals in March/April – and our job now is to reduce the size of this wave over the winter!
You’ll all have seen wide variety of masks and face coverings worn in a wide (and often alarming!) variety of ways. Leaving aside the (in)correct wearing of masks, it’s useful to see some comparative data on the relative respiratory protection offered by different mask materials. This study, published years ago (pre COVID!), does just that.
There are rumblings that glove wearing (aka “hand coverings“) are being considered as a widespread recommendation to prevent the spread of SARS-CoV-2 in public places (e.g. shops) in the UK. The message of this post is simple – please, no gloves. Convincing clinical staff of the unintended consequences of glove overuse is tricky enough. But widespread use of gloves in public places like shops may just bring me to tears. (Unless anybody can point me in the direction of solid evidence that this is likely to have a net benefit in reducing transmission…!).
We have just had a study published in Clinical Infectious Diseases exploring the extent and magnitude of hospital surface and air contamination with SARS-CoV-2 during the (first!) peak of COVID-19 in London. The bottom line is that we identified pretty extensive surface and air contamination with SARS-CoV-2 RNA but did not culture viable virus. We concluded that this highlights the potential role of contaminated surfaces and air in the spread of SARS-CoV-2.
The next instalment of the HIS audience-led webinar series is on the role of contaminated surfaces in COVID-19 transmission. I was delighted to be part of the panel for this one:
- Dr Lena Ciric – Associate Professor in Environmental Engineering, University College London
- Dr Stephanie Dancer – Consultant Microbiologist, NHS Lanarkshire and Professor of Microbiology, Edinburgh Napier University, Scotland
- Dr Manjula Meda – Consultant Clinical Microbiologist and Infection Control Doctor, Frimley Park Hospital
- Dr Jon Otter – Infection prevention and control Epidemiologist, Imperial College London
- Chair: Dr Surabhi Taori, Consultant microbiologist and infection control doctor, Kings College Hospital NHS Foundation Trust
Here’s the recording:
The next in the series of the HIS audience-led webinar on all-things ventilation in the management of COVID-19 went out recently. The panel consisted of:
- Peter Hoffman – Consultant Clinical Scientist, London
- Dr Chris Lynch – Graham Ayliffe Training Fellow, Sheffield Teaching Hospitals
- Professor Catherine Noakes – Professor of Environmental Engineering for Buildings, University of Leeds
- Karren Staniforth – Clinical Scientist, Nottingham University Hospitals NHS Trust
- Dr James Price (chair) – Consultant in Infection Prevention & Control and Antimicrobial Stewardship, Imperial College Healthcare NHS Trust
The webinar video is below:
There’s a huge amount of academic and pragmatic discussion and debate about the appropriate levels of PPE to wear in various healthcare settings to reduce the risk of spreading COVID-19 to yourself and others in healthcare settings. And more recently, when to wear face coverings / masks / shields in public areas of hospitals, on public transport, and in shops. However, there is much, much less discussion about the importance of careful doffing (removal) of PPE and face coverings etc in order to ensure the safe and effective use of PPE. This helpful Cochrane Review, updated for the COVID-19 era, covers a lot of ground and one key conclusion is that doffing is key: if it is done carefully, the risk of self-contamination is lower.