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The data published by the John Hopkins University report a sharp spike in new detected cases of SARS-CoV2 infections in France for two days ago (April 4), with 25000 new people tested positive in one day, a number that is an order of magnitude larger than their usual daily counts:

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This raises their total to 93k confirmed cases. These numbers contrast with those given by official French sources, see e.g. here

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I do not have better historic French data here unfortunately, but the point is that these two numbers were in the same ballpark (fewer than 70k total infections dtected) up to two days ago, but now they differ substantially due to that spike.

See also this plot on Wikipedia, which cites French sources (I cannot locate numbers directly on the linked page [16])

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These numbers match reasonably well the JHU cumulative data up to April 4, but then they diverge.

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Is the April 4 spike in the JHU data real? Is it maybe due to the JHU data "catching up" with a new definition of new cases? Is it a practical error (e.g., one more zero in the numbers reported in some regions)?

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  • In any case, these are not 'infections', but 'cases with positive test results'. While 'true number infections' is much higher, this number above also consists of false positives… JHU numbers are also quite unreliable in general as they favour speed, 'diversity of sources' and 'high numbers', over reliable numbers, which are lower & slower.
    – LangLаngС
    Apr 6, 2020 at 10:39
  • @LаngLаngС Thanks for the observation. I have edited the question putting more emphasis on the fact that these are detected cases.
    – Federico Poloni
    Apr 6, 2020 at 10:43
  • Could easily be explained by an increase in testing rate, or the release of a backlog of test results.
    – Daniel R Hicks
    Apr 6, 2020 at 11:38
  • @DanielRHicks An increase in testing rate or a backlog in test results does not explain, alone, the discrepancy between these two data sources. Anyway, my question is to explain it...
    – Federico Poloni
    Apr 6, 2020 at 11:44
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    It takes several days to validate and incorporate the data. At this point the data is an extremely "unresolved current event" and hence not suitable fodder for this site.
    – Daniel R Hicks
    Apr 6, 2020 at 12:02

1 Answer 1

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Spikes like this in reported cases are not unusual, see also this graph for China and the explanation for it. There can be various reporting "bottlenecks" that suddenly report backlogged tests.

In France, what seems to have happened on April 3-4 (as Reuters reported):

The number of people who have died from the COVID-19 illness in France jumped by 61% to 6,507 over two days after data from nursing homes were included, and confirmed cases jumped by 44% to 82,165, the health ministry reported on Friday, making France the fifth country to report more cases than China.

Salomon also reported a total of 17,827 confirmed or suspected cases in nursing homes, compared to 14,638 on Thursday, when the nursing home data were first reported.

By including the nursing home data, France now has a total of 82,165 confirmed or suspected cases. It joined the United States, Spain, Italy and Germany as nations that have now surpassed cases reported by China, where the pandemic originated, according to a Reuters tally. [...]

Following criticism about French COVID-19 statistics not reflecting the dozens of people dying in senior citizens’ residences or their own homes, the health ministry on Thursday provided the first data on deaths in nursing homes.

A far as JHU vs official santepubliquefrance.fr (SP.FR henceforth) is concerned, they indeed appear to diverge on "total cases", but the explanation for that is that the left upper "cyan box" in the French dashboard ("confirmed cases") is still showing just the hospital-confirmed cases. You need to add the bottom right, dark blue box "CAS en ESMS" for the cases in nursing homes, which also has a sub-field for deaths therein. (Thanks to @Relaxed for pointing out this; a previous version of this answer incorrectly said that you needed to add the "closed" hospital cases [return home] (green upper-right box), but while those numbers were closer to the ESMS ones yesterday, today there's 10K difference today, which makes my prior explanation clearly wrong in that respect.)

This can be double-checked in a way by looking at a 3rd source, worldometers.info, which cites SP.FR as their data source, but presents the info much more like JHU, i.e. worldometers adds the ESMS cases to the hospital ones. Three large screencaps follow:

enter image description here enter image description here enter image description here

So, SP.FR "total cases" = hospital-confirmed (78,167) + ESMS (30,902) = 109,069 == worldometers total. JHU total: 110,070 (pretty close). Deaths: SP.FR "red box" 10,328 == worldometers deaths. JHU deaths: 10,343, pretty close. ("Recoverd" case, i.e. returns from hospital is also largely in agreement 19.5K JHU vs 19.3K SP.FR/worldometers)

The same worldometers page also makes it clear that the (Apr 3) Reuters-reported spike was real/substantial (that graph is from yesterday):

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So in summary: yes there was a spike in reported cases (even by the French) due a change in their methodology (including nursing homes) on April 3, and additionally the SP.FR page still separates total cases in hospital-confirmed and ESMS ones...

(I'm still not sure exactly how SP.FR adds the deaths since the ESMS death sub-field is 4K, but their "red box" has 7K hospital deaths... while the red-box total is only 10.3K.)

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    Thanks; this explains things perfectly.
    – Federico Poloni
    Apr 7, 2020 at 7:10
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    The total case count on the worldometer website is equal to the "cas confirmés" + "cas en ESMS" on the SPF dashboard (which is quite arbitrary). According to the detailed briefings available on the website, the “cas confirmé“ estimate is based on data from testing labs and hospitals. There is no indication that closed cases have been subtracted but, in light of the new testing guidelines, SPF doesn't consider its “confirmed case“ count a good indicators of the number of infections in France.
    – Relaxed
    Apr 8, 2020 at 9:10
  • @Relaxed: I see, it was a coincidence that "closed cases" nearly equaled the "ESMS" ones; I'll revise the answer a bit later... (In fact I don't mind at all if you post your own on that part).
    – Fizz
    Apr 8, 2020 at 9:14
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    Note that the daily briefings and media commentary in France focus almost exclusively on the number of deaths, ICU and hospital admissions, not estimates of the total number of cases (confirmed or otherwise).
    – Relaxed
    Apr 8, 2020 at 9:14
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    @FedericoPoloni and Fizz: The SPF dashboard has been updated again to clarify the difference between the different counts. As of today, they recorded 12210 deaths of which 8044 in hospitals and 5241 from EMS residents of which 4166 inside the facilities themselves (so 1075 people living in an EMS were apparently transferred to hospital before dying there, which would explain the earlier discrepancies). Note that “EMS” includes various types of nursing homes but also shelters for asylum seekers or homeless people, institutions for adults suffering from intellectual disabilities, etc.
    – Relaxed
    Apr 10, 2020 at 12:27

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