HSE outlines 5 per cent Covid-19 positivity rate assumption

A 5 per cent national positivity rate for Covid-19 testing, as assumed in the HSE’s Winter Plan, is based on data from the Epidemiological Modelling Advisory Group (IEMAG) and positivity rate patterns in population cohorts tested to date, a HSE spokesperson has told the Medical Independent (MI).

“The HSE has been using a range of different projections to estimate testing volumes and testing demand to support scenario analysis and scenario planning. It relies on data from the IEMAG and also examines positivity rate patterns on cohorts of the population tested to date. To inform this paper [the winter plan] a mid-range estimate was used (between 2 per cent and 10 per cent) to assess likely demand for different parts of the service,” outlined the HSE’s spokesperson.

A proposed testing model in the winter plan assumes 10,000 tests daily in the community (9,000 via GP referral and 1,000 via a “central clinically governed team”) and 5,000 in acute settings.

A positivity rate of 5 per cent of the 10,000 community referrals is assumed, which would equate to 500 positive results per day in the community. The overall plan covers the period from October 2020 to April 2021.

To date, the peak positivity rate in all Covid-19 testing for the previous seven days was 23.2 per cent, as recorded on 3 April. Before mid-June, this metric had dropped to less than 1 per cent, falling to just 0.2 per cent in early July. On 1 September, the positivity rate for the previous seven days was 1.2 per cent and this had risen to 3.1 per cent on 1 October.

At press time for MI’s hard copy publication, the rate was 3.9 per cent and rising. On the day of online publication, the figure was 5.5 per cent.

According to an article by the Bloomberg School of Public Health at Johns Hopkins, US, “as a rule of thumb” one threshold for the positivity percentage being ‘too high’ is 5 per cent.

“For example, the World Health Organisation recommended in May that the per cent positive remain below 5 per cent for at least two weeks before governments consider reopening.”