The number of confirmed cases for COVID-19 is dramatically understated due to insufficient testing

The number of confirmed cases for the novel coronavirus disease COVID-19 officially issued by countries and widely commented on by national and international media outlets dramatically understates the true number of infections, a recent report from the University of Göttingen suggests.

Dr Christian Bommer and Professor Sebastian Vollmer from Göttingen University have used estimates of COVID-19 mortality and time until death from a recent study published in The Lancet Infectious Diseases to test the quality of official case records.

Their data shows that countries have only discovered on average about 6% of coronavirus infections and the true number of infected people worldwide may already have reached several tens of millions.

Insufficient and delayed testing may explain why some European countries, such as Italy and Spain, are experiencing much higher casualty numbers (relative to reported confirmed cases) than Germany, which has detected an estimated 15.6% of infections compared to only 3.5% in Italy or 1.7% in Spain.

Detection rates are even lower in the United States (1.6%) and the United Kingdom (1.2%) – two countries that have received widespread criticism from public health experts for their delayed response to the pandemic.

In sharp contrast to this, South Korea appears to have discovered almost half of all its SARS-CoV-2 infections.

By early spring, Europe had become the worst-affected region, with Italy and Spain particularly hard hit. However, differences in testing mean that the number of cases may be understated for some countries.

Confirmed cases of Covid-19 for selected countriesShowing the number of cases since the day of the 100th case, using a log scale. Data correct at 23.59 UTC 6 April

The number of deaths is a more dependable indicator. The disease is hitting Italy and Spain with particular cruelty. But the trajectory in many countries is the same; the UK and US are a couple of weeks behind Italy in the progress of the epidemic.

Confirmed deaths of Covid-19 for selected countriesShowing the number of deaths since the day of the first one, using a log scale. Data correct at 23.59 UTC 6 April

Meanwhile in Asia, where the disease began, the spread continues, although in China it seems for now to have passed its peak.

The authors estimate that on 31 March 2020, Germany had 460,000 infections. Based on the same method, they calculate that the United States had more than ten million, Spain more than five million, Italy around three million and the United Kingdom around two million infections.

On the same day the Johns Hopkins University reported that globally there were less than 900,000 confirmed cases, meaning that the vast majority of infections were undetected.

Sebastian Vollmer, Professor of Development Economics at the University of Göttingen, says, “These results mean that governments and policy-makers need to exercise extreme caution when interpreting case numbers for planning purposes.

Such extreme differences in the amount and quality of testing carried out in different countries mean that official case records are largely uninformative and do not provide helpful information.”

Christian Bommer adds: “Major improvements in the ability of countries to detect new infections and contain the virus are urgently needed.”

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I would like to analyze a very interesting case, in which the danger of the asymptomaticity of COVID-19 is evident!

An outbreak of coronavirus disease 2019 (COVID-19) unfolded on board a Princess Cruises’ ship called the Diamond Princess.

Shortly after arriving in Yokohama, Japan, this ship had been placed under quarantine orders from 5 February 2020, after a former passenger had tested positive for the virus responsible for the disease (i.e. severe acute respiratory syndrome coronavirus 2; SARS-CoV-2), subsequent to disembarking in Hong Kong.

In this study, we conducted a statistical modelling analysis to estimate the proportion of asymptomatic individuals among those who tested positive for SARS-CoV-2 on board the ship until 20 February 2020 included, along with their times of infections.

The model accounted for the delay in symptom onset and also for right censoring, which can occur due to the time lag between a patient’s examination and sample collection and the development of illness.

Epidemiological description and data

By 21 February 2020, 2 days after the scheduled 2-week quarantine came to an end, a total of 634 people including one quarantine officer, one nurse and one administrative officer tested positive for SARS-CoV-2.

These individuals were among a total of 3,711 passengers and crew members on board the vessel.

Laboratory testing by PCR had been conducted, prioritising symptomatic or high-risk groups.

Daily time series of laboratory test results for SARS-CoV-2 (both positive and negative), including information on presence or absence of symptoms from 5 February 2020 to 20 February 2020 were extracted from secondary sources [1].

The reporting date, number of tests, number of persons testing positive by PCR (i.e. cases) and number of symptomatic and asymptomatic cases at the time of sample collection are provided, while the time of infection and true asymptomatic proportion are not available.

A total of 634 people tested positive among 3,063 tests as at 20 February 2020.

Of 634 cases, a total of 313 cases were female and six were aged 0–19 years, 152 were aged 20–59 years and 476 were 60 years and older (Figure).

Cases were from a total of 28 countries, with most being nationals of six countries, namely Japan (n = 270 cases), the United States (n = 88 cases), China (n = 58 cases; including 30 from Hong Kong), the Philippines (n = 54 cases), Canada (n = 51 cases) and Australia (n = 49 cases).

Of the 634 confirmed cases, a total of 306 and 328 were reported to be symptomatic and asymptomatic, respectively.

The proportion of asymptomatic individuals appears to be :

• 16.1% (35/218) before 13 February,
• 25.6% (73/285) on 15 February,
• 31.2% (111/355) on 16 February,
• 39.9% (181/454) on 17 February,
• 45.4% (246/542) on 18 February,
• 50.6% (314/621) on 19 February and
• 50.5% (320/634) on 20 February (Table).

Soon after identification of the first infections, both symptomatic and asymptomatic cases were transported to designated medical facilities specialised in infectious diseases in Japan.

However, these patients were treated as external (imported) cases, and a detailed description of their clinical progression is not publicly available.

Table

Data on characteristics, test results for severe acute respiratory syndrome coronavirus 2, and disembarking of passengers and crew of the Diamond Princess cruise ship, Yokohama, Japan, February 2020 (n = 3,711)

Date (2020)a	Number of passengers and crew members on board	Number of disembarked passengers and crew members (cumulative)	Number of tests	Number of tests (cumulative)	Number of individuals testing positive	Number of individuals testing positive (cumulative)	Number of symptomatic cases	Number of asymptomatic cases	Number of asymptomatic cases (cumulative)
5 Feb	3,711	NA	31	31	10	10	NA	NA	NA
6 Feb	NA	NA	71	102	10	20	NA	NA	NA
7 Feb	NA	NA	171	273	41	61	NA	NA	NA
8 Feb	NA	NA	6	279	3	64	NA	NA	NA
9 Feb	NA	NA	57	336	6	70	NA	NA	NA
10 Feb	NA	NA	103	439	65	135	NA	NA	NA
11 Feb	NA	NA	NA	NA	NA	NA	NA	NA	NA
12 Feb	NA	NA	53	492	39	174	NA	NA	NA
13 Feb	NA	NA	221	713	44	218	NA	NA	NA
14 Feb	3,451	260b	NA	NA	NA	NA	NA	NA	NA
15 Feb	NA	NA	217	930	67	285	29	38	73c
16 Feb	NA	NA	289	1,219	70	355	32	38	111
17 Feb	3,183	528b	504	1,723	99	454	29	70	181
18 Feb	NA	NA	681	2,404	88	542	23	65	246
19 Feb	NA	NA	607	3,011	79	621	11	68	314
20 Feb	NA	NA	52	3,063	13	634	7	6	320

The asymptomatic proportion was defined as the proportion of asymptomatically infected individuals among the total number of infected individuals.

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Source:
University of Gottingen