How to navigate the Covid-19 indicators?

AFP, published Thursday 12 November 2020 at 12:39

How to navigate the jungle of Covid-19 indicators? The media and the general public are flooded every day with figures that are not always easy to interpret. Here is a guide to see more clearly.

. HOW MANY CASES?

The French Public Health Agency (SpF) publishes a series of new confirmed cases of Covid-19 every day in the last 24 hours. Also available on the TousAntiCovid app, this figure, which rose to over 60,000 last Friday – a record – to drop between 20,000 and 35,000 between Monday and Wednesday, reveals the number of additional cases registered in the national Sidep (Population Screening Information System) database. ).

But “this does not mean that these people have been captured in the past 24 hours,” SpF told AFP. The results, in fact, can be recorded with a few days delay and correspond to laboratory tests of several days before, therefore to even earlier contaminations. The system was disrupted last week by a computer jam, and no data was released this weekend.

Every Thursday, SpF also broadcasts a weekly positive test count for the previous two weeks, which leads to different results and allows for greater perspective. Thus, 333,305 tests were positive the week of October 26, 273,566 the previous week, 168,772 cases two weeks earlier. Again, these data consolidate over time.

In any case, these indicators reflect only the status of the positive tests, a necessarily very incomplete picture of the actual contaminations. A significant percentage of people with Covid-19 don’t develop symptoms and don’t necessarily get tested.

. POSITIVITY AND INCIDENCE RATES

The positive rate measures the percentage of positive cases out of the number of tests. Main advantage: don’t settle for a gross number of new cases, which can increase or decrease because there are more or less tests. At less than 5% in early September, this rate has risen to 20% in recent days nationwide.

But even here, beware of prejudices. This figure “does not represent the frequency of virus transport in the French population, but transport in the population tested”, which has more “symptomatic people and people in contact with symptoms”, warns epidemiologist Catherine Hill.

The incidence rate provides the number of new cases detected over seven days per 100,000 population. Again, we only measure what we test. In France, the incidence rate was still below 100 (96.2) the week of September 7 (out of a total of nearly 1.4 million tests) versus 497 the week of October 26 (for 2.1 million tests ), before starting to decline nationwide. Also in this case it will be necessary to wait a few days to consolidate the data.

. LE R

The “R effective” is the estimated reproductive rate of the virus, which is the estimated average number of people a patient infects. It is calculated from the number of positive tests or emergency visits or hospitalizations for Covid-19.

If it is greater than 1, it means that the trend is upward in the number of cases. If the R is less than 1, “the epidemic is on the decline”. But as Spf specifies, it is “an indicator of the dynamics of virus transmission approximately 1 to 2 weeks earlier (integrating the time between contamination and testing, and the fact that the calculation is performed over a period of 7 days)”.

In its bulletins, the agency invites us not to interpret these data “in isolation”, but to put them in perspective “with the other epidemiological data available”.

In its latest bulletin, dated Monday, SPF provides estimates for the week of October 18 to 24, with an actual R of around 1.3. TousAntiCovid shows a more optimistic trend on Thursday morning (0.93), an estimate based on more recent data (as of November 7) but less consolidated.

. ENTRANCE TO HOSPITAL AND RESUSCITATION

For all experts, the decrease in hospitalizations for several days will necessarily translate into a decrease in the circulation of the virus from one to two weeks earlier, the presumed time between the time you are infected and the time when symptoms occur . get worse. At this stage, this is not the case. There have been 17,450 new hospital admissions in the past seven days on November 1, then 18,866 on November 4, and between 19,000 and 20,000 since then, before a drop on Wednesday (18,828) that remains to be confirmed.

The rate of admissions to intensive care services is also increasing, with 2,605 new arrivals in the last seven days on 1 November, 2,884 in the same period on 4 November and over 3,000 since 7 November, except Wednesday (2,906).

With a total of 4,789 patients in these wards, the occupancy rate of available beds in the ICU is displayed at 94.7% on the TousAntiCovid application. Please note, however, that this rate is calculated from the total number of beds in “starting capacity”, ie approximately 5,000. The government last week published a capacity of 6,544 beds, which was to be further increased to 7,700 and then to 10,500 beds.

. HOW MANY DEAD?

Public Health France reports the number of hospital deaths of patients with Covid-19 every day, adding to it, on Tuesdays and Fridays, deaths in nursing homes. The daily number of hospital deaths reached 551 on Monday, the highest since the second wave began. In total, the death toll rises according to SpF to 42,535, of which almost 30,000 in hospitals, the rest in nursing homes and other medical-social institutions.

These figures do not include home deaths, estimated at nearly 1,900 between March 1 and May 31, according to Inserm’s still provisional figures at the end of August.