To the Editor — In December 2019, a novel coronavirus was isolated, after a cluster
of patients in China were diagnosed with pneumonia of unknown cause
1
. This new isolate was named ‘SARS-CoV-2’ and is the cause of the disease COVID-19.
The virus has led to an ongoing outbreak and an unprecedented international health
crisis. The number of infected people is rapidly increasing globally
2
and most probably is a vast underestimation of the real number of patients worldwide,
as infected people are contagious even when minimally symptomatic or asymptomatic
3
. The spread of the disease has presented an extreme challenge to the international
community, and policy-makers from different countries have each chosen different strategies,
depending on the local spread of the virus, healthcare-system resources, economic
and political factors, public adherence, and their perception of the situation.
Coronavirus infection spreads in clusters, and early identification of these clusters
is critical for slowing down the spread of the virus. Here we propose that daily population-wide
surveys that assess the development of symptoms caused by the virus could serve as
a strategic and valuable tool for identifying such clusters and informing epidemiologists,
public-health officials and policymakers. We show preliminary results from an Israeli
survey of a cumulative number of over 74,000 responses and call for additional countries
to join an international consortium to extend this concept in order to develop predictive
models. We expect such data will allow the following: faster detection of spreading
zones and patients; acquisition of a current snapshot of the number of people in each
area who have developed symptoms; prediction of future spreading zones several days
before an outbreak occurs; and evaluation of the effectiveness of the various social-distancing
measures taken and their contribution to reducing the number of symptomatic people.
This information could provide a valuable tool for decision-makers in those areas
in which strengthening of social-distancing measures is needed and those in which
such measures can be relieved. Preliminary analysis shows that in neighborhoods with
a confirmed patient history of COVID-19, more people report experiencing COVID-19-associated
symptoms, which demonstrates the potential utility of our approach for the detection
of outbreaks. Researchers from other countries, including the USA, UK, Canada, Switzerland,
Germany, and several others are working on similar projects, such as the COVID Symptom
Tracker in the UK
4
. We call with urgency for other countries to join our international consortium
5
, and to share methods and data collected from these daily, simple, one-minute surveys.
In Israel, the first infection of COVID-19 was confirmed on 21 February 2020, and
in response, the Israeli Ministry of Health (MOH) instructed people who returned to
Israel from specific countries in which COVID-19 was spreading to go into a 14-day
home isolation. Since then, Israel has gradually imposed several additional measures
(Extended Data Fig. 1): on 9 March, the 14-day home isolation was extended to people
arriving from anywhere of international origin, and those who were in close contact
with a patient with confirmed COVID-19 were instructed similarly. Symptomatic people
were instructed to stay home for 2 days after symptom resolution
6
. On 11 March, gatherings were limited to a maximum of 100 people; this was further
restricted to 10 people on 15 March. On 19 March, a national state of emergency was
declared in the country. On 20 March, the first death of an Israeli citizen from COVID-19
occurred.
One of the main challenges of the current pandemic so far has been disease detection
and diagnosis. Although the gold standard for the diagnosis of COVID-19 is detection
of the virus by a real-time PCR testing
7
, current resource and policy limitations in many countries restrict the amount of
testing that can be performed. The number of tests per day is increasing; however,
not enough tests are being performed to provide a nationwide view of the spread of
the virus, particularly as the Israeli MOH guidelines are to test only people who
were in close contact with a person with confirmed COVID-19.
To obtain a real-time nationwide view of symptoms across the entire population, and
since testing the entire population is not feasible, we developed a simple one-minute
online questionnaire aimed at early and temporal detection of geographic clusters
in which the virus is spreading. The survey was posted online (https://coronaisrael.org/)
on 14 March, and participants were asked to fill it out on a daily basis and separately
for each family member, including members who are unable to fill it out independently
(e.g., children and older people). So that potential privacy issues that might occur
can be avoided, our survey is filled out anonymously, and access to the data is restricted
to only study investigators.
The survey contains questions on age, sex, geographic location (city and street),
isolation status and smoking habits. Participants also report whether they are experiencing
symptoms commonly described in patients with COVID-19 by healthcare professionals,
on the basis of the existing literature
8
. Several other symptoms that are less common in patients with COVID-19 but are more
common in other infectious diseases are also included to better identify possible
patients with COVID-19. The initial symptoms included cough, fatigue, myalgia (muscle
pain), shortness of breath, rhinorrhea or nasal congestion, diarrhea and nausea or
vomiting. Additional symptoms, including type of cough (with or without sputum), sore
throat, headache, chills, confusion and loss of taste and/or smell sensation, were
added in a later version. Participants also report about existing chronic health conditions
and are asked to report their daily body temperature (Extended Data Fig. 2 presents
the most recent version of the survey).
Given that reports on the clinical characteristics of patients with COVID-19 are only
starting to emerge, we defined an initial basic measure we called the ‘symptoms ratio’
using symptoms that were predefined by the Israeli MOH and are commonly reported by
patients with COVID-19
8
. Symptoms assessed were shortness of breath, fatigue, cough, muscle pains and fever
(body temperature above 38 °C). For participants younger than 18 years of age, nausea
and/or vomiting was also included in the ratio calculation. For each participant,
the symptoms ratio was calculated as the number of reported symptoms divided by the
number of symptoms in our predefined list (number of reported symptoms / 6, for participants
18 years of age or less; number of reported symptoms / 5, for participants over 18
years of age). We plan to refine this list of symptoms as more clinical information
is accrued. By associating participants with an area corresponding to their address,
we created a color map of Israel by the aggregated symptoms ratio in each neighborhood
(Fig. 1).
Fig. 1
Average COVID-19-associated symptoms region map.
City municipal regions with at least 30 completed surveys and neighborhoods with at
least 10 completed surveys are shown. The color of each region indicates a category
defined by the average symptoms ratio, calculated by averaging the reported symptoms
rate by responses in that city or neighborhood. The values were divided into five
categories, and the color of each region indicates its associated category, from green
(low symptom rate) to red (high symptom rate) (key). a, Area of Tel-Aviv and Gush-Dan
with city regions. b, Area of Tel-Aviv and Gush-Dan with neighborhood regions. Map
data are copyrighted by OpenStreetMap contributors and are available from https://www.openstreetmap.org.
Publ. note: Springer Nature is neutral about jurisdictional claims in maps.
Leaflet | OpenStreetMap contributors | CARTO
The questionnaire was first distributed online on 14 March 2020, at 14:43 Israel Standard
Time (Greenwich Mean Time + 2 hours), and was disseminated through social media and
traditional press media. As of 23 March, 18:00 Israel Standard Time, a cumulative
number of 74,256 responses had been received from 69,386 adults (93.44%) and 4,870
children (6.56%) (participant characteristics, Table 1). Of these, 3,007 respondents
(4.05%) reported that they were currently in isolation, of which 1,458 (48.49%) were
in isolation due to a recent international travel and 1,549 (51.51%) were in isolation
due to a contact with a person with COVID-19 or a person who recently returned from
abroad. A new version of the questionnaire was established on 21 March, driven by
new policies implemented by the Israeli MOH (Extended Data Fig. 1) and accumulating
data on patients’ symptoms
8
. The updated version includes several more questions (Extended Data Fig. 2) and has
not been distributed yet.
Table 1
Characteristics of questionnaire responses
Characteristic (mean (s.d.) or %)
All(n = 74,256)
No in-home isolation(n = 71,249)(95.95%)
In-home isolation(n = 3,007)(4.05%)
Adults(n = 69,386)(93.44%)
Children(under 18 years of age)(n = 4,870) (6.56%)
Age (years)
45.38 (18.21)
45.54 (18.22)
41.58 (17.57)
47.73 (16.41)
11.95 (5.19)
Male
34,575 (46.56%)
33,085 (46.44%)
1,490 (49.55%)
32,108 (46.27%)
2,467 (50.66%)
Smoking history (previously smoked or currently smoking)
27,003 (36.36%)
25,990 (36.48%)
1,013 (33.69%)
26,814 (38.64%)
189 (3.88%)
Presence of a chronic medical conditions
15,102 (20.34%)
14,622 (20.52%)
480 (15.96%)
14,850 (21.4%)
252 (5.17%)
Symptoms
No symptoms (feel good)
61,999 (83.49%)
59,592 (83.64%)
2,407 (80.05%)
58,191 (83.87%)
3,808 (78.19%)
Body temperature
36.5 °C (0.45)
36.49 °C (0.45)
36.53 °C (0.48)
36.49 °C (0.43)
36.62 °C (0.65)
Body temperature ≥38 °C
227 (0.31%)
196 (0.28%)
31 (1.03%)
130 (0.19%)
97 (1.99%)
Nausea and vomiting
433 (0.58%)
407 (0.57%)
26 (0.86%)
373 (0.54%)
60 (1.23%)
Myalgia (muscle pain)
2,359 (3.18%)
2,229 (3.13%)
130 (4.32%)
2,231 (3.22%)
128 (2.63%)
Rhinorrhea or nasal congestion
9,807 (13.21%)
9,384 (13.17%)
423 (14.07%)
8,804 (12.69%)
1,003 (20.6%)
Fatigue
3,014 (4.06%)
2,845 (3.99%)
169 (5.62%)
2,804 (4.04%)
210 (4.31%)
Shortness of breath
1,430 (1.93%)
1,331 (1.87%)
99 (3.29%)
1,343 (1.94%)
87 (1.79%)
Cough
10,089 (13.59%)
9,597 (13.47%)
492 (16.36%)
9,232 (13.31%)
857 (17.6%)
Diarrhea
1,286 (1.73%)
1,198 (1.68%)
88 (2.93%)
1,145 (1.65%)
141 (2.9%)
Symptoms ratio
Symptoms ratio
0.05 (0.11)
0.05 (0.11)
0.06 (0.14)
0.05 (0.11)
0.05 (0.11)
The symptoms ratio (bottom row) was calculated as the number of reported symptoms
divided by the number of symptoms in the predefined Israeli MOH symptoms list.
We attempted to reach all sectors of the Israeli population in distributing the survey―first,
by translating and distributing it in five languages (Hebrew, Arabic, English, Russian
and Amharic) that reflect the most common languages spoken in Israel. Second, we are
devoting efforts to reach underrepresented populations through several channels, including
call centers, media appearance and promotion of the survey through Arabic—speaking
television stations to gain interest and compliance in all sectors of the population.
We analyzed the symptoms ratio of participants by geographical location in Israel
(Fig. 1). This analysis revealed differences in the proportion of reported symptoms
in participants from different cities and different neighborhoods that are geographically
close to each other, which might suggest the ability to detect changes at high geographical
resolution.
We also analyzed the association between the prevalence of symptoms reported in the
survey and the prevelence of the same symptoms in patients with COVID-19
8
. We then integrated data from the Israeli MOH on the locations of known COVID-19
cases and divided the responses into two groups depending on whether they were living
in neighborhoods in which confirmed cases were present or not. Notably, in neighborhoods
in which people with confirmed COVID-19 were present, we detected a higher prevalence
of symptoms that were highly prevalent in patients with confirmed COVID-19 (e.g.,
cough) and lower rates of symptoms that were less prevalent (e.g., rhinorrhea), which
demonstrates the potential of our method for detecting disease clusters at high geographical
resolution (Fig. 2).
Fig. 2
Symptom prevalence.
Prevalence of symptoms for survey responses from neighborhoods in which confirmed
cases were present (red) or no confirmed cases were present (blue), presented as estimates
and 95% confidence intervals of patients with COVID-19 from a published meta-analysis
8
(x axis) plotted against prevalence from survey data and bootstrap estimates of 95%
confidence intervals (y axis); dashed diagonal line, y = x.
In conclusion, we have developed a short survey based on symptoms associated with
COVID-19 with the primary goal of early detection of clusters of COVID-19 outbreak.
At the time of this writing, only 10 days after the survey was first distributed,
74,256 responses had been received. As expected, we also detected a higher percentage
of symptoms among people who were in home isolation than among those who were not
(0.06 and 0.05, respectively; P = 5 × 10–14 (two-sample t-test)).
Although the spread of COVID-19 is exponential
9
, and the number of patients with confirmed COVID-19 in Israel has increased from
193 on 14 March to 1,238 on 23 March
10
, it has yet to reach the vast majority of Israel’s population. Thus, it is possible
that our measured symptoms could be reflective of other conditions (such as influenza)
that were prevalent in Israel during this period, as many diseases share common symptoms
11
.
Our tool has several potential applications. Although it does not have the ability
to diagnose individual cases of COVID-19, it might help to predict future spreading
zones a few days before an outbreak occurs, with a high level of accuracy, given a
sufficient sample size. Here we have provided a color map of Israel by regions of
symptoms ratio (Fig. 1), but as the daily response rate increases, we expect to derive
predictive models. We anticipate that these would be leveraged by policymakers to
make informed decisions through the utilization of efficient regional prevention strategies
rather than a uniform approach. Our survey might also be used to evaluate the effectiveness
of prevention strategies implemented by public-health organizations, such as the various
social-distancing measures that are currently being implemented in many countries,
including Israel
12
. This can be done by measuring the effect of different strategies on reducing the
number of symptomatic people. Finally, it might help in elucidating the clinical course
of COVID-19 by tracking the dynamics of symptoms in the population over time.
Addressing the ongoing needs of the medical and scientific community, as well as feedback
from policymakers, will drive the direction and focus of our future work. To improve
ease of use by participants and streamline the data-collection process, we are also
building a designated mobile application that will be finalized and rolled out as
soon as it is available. We also plan to resolve privacy issues around location sharing
in the future application, data for which will be used only at an aggregated level
and can substantially improve our models, and provide valuable insights on population
interactions, adherence and disease-spread dynamics.
Our approach has many possible clinical implications; however, we have also encountered
several challenges. Given that participants will be asked for personal medical information,
there are concerns about identification and potential misuse of information. As mentioned
above, we ask participants to fill out the survey anonymously, but we do ask for address
details. These data are accessible only by the study investigators, and we are investing
resources in properly securing the data to ensure that the privacy rights of our participants
will be protected. Since our survey is anonymous, we cannot link the same participant’s
daily questionnaires, which could provide individual trends as we proceed. Another
major challenge with the type of data we collect is that it is prone to selection
bias. We observe that regions with relatively high response rate are regions associated
with higher socioeconomic status. Some bias may decrease as these surveys become more
widely used and thus better reflect the true population; we intend to model and adjust
for different factors such as age and location, and to implement national socioeconomic
indices, in future analyses.
We urge other countries to adopt this tool and encourage their populations to use
these daily, simple, one-minute surveys. We call for an international collaboration
that will allow the sharing of methods and collected data. We also call for the large
technology and social-media companies already collecting elements of personal data
to collaborate in this international effort by sharing regional information to help
us improve our models.
Ethics declaration
The study protocol was approved by the institutional review board (IRB). Informed
consent was waived by the IRB, as all identifying details of the participants were
removed before the computational analysis. Participants were made fully aware of the
way in which the data will be stored, handled and shared, which was provided to them
and is in accord with the privacy and data-protection policy of the Weizmann Institute
of Science (https://weizmann.ac.il/pages/privacy-policy).
Reporting Summary
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