Coronavirus disease (COVID-19) technical guidance by WHO Investigation protocol for COVID-19 | Page 6

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Two or more people living together in a domestic residence (residential institutions, such as
boarding schools, dormitories, hostels or prisons will be excluded).
A dwelling or group of dwellings with a shared kitchen or common opening onto a shared
household space.
All persons living in the household should be invited to participate in the study, including children to
ensure age-specific attack rates can be calculated.
COMMENT: The distribution of household compositions in the population would be needed to
calculate population, age-specific infection attack rates.
The random selection of households within a geographic area is one method of recruitment.
Random digit dialing 1 , blood donors or other ongoing longitudinal cohort studies may also be used
to identify and recruit individuals to participate in the investigation. The advantage of working with
blood donors is that they are usually forthcoming to being contacted for future follow-up and you
may be able to track long-term antibody dynamics. For COVID-19, the age-specific attack rates in
blood donors are likely to be similar to that in the general population except for those with
substantial comorbidities or elevated exposure (e.g. healthcare workers).
COMMENT: Plasma may be collected from a subset of participants so that the serologic assay results
of the serum and plasma could be compared. This might be useful if sera and plasma give the same
results as plasma are stored in many blood donor archives which could be used to retrospectively to
estimate the infection attack rate.
Whichever method is used to identify and recruit participants, all attempts should be made to
include participants over a range of ages in order to be able to determine and compare age-specific
attack rates, although crude age-specific estimates will need to be adjusted for age structures in the
population.
COMMENT: Depending on which method of study recruitment is chosen, the group implementing
the study may choose either to conduct home visits to collect data and specimens or to centralize
data and specimen collection at one location, asking participants to travel to the location to
participate in the study. Decisions as to how to implement the study should be determined by
feasibility and resource (including personnel) availability.
2.3 Eligibility criteria
Inclusion criteria: All individuals identified for recruitment into the investigation, irrespective of age.
Exclusion criteria: Refusal to give informed consent, or contraindication to venipuncture.
COMMENT: Suspected or confirmed acute or prior COVID-19 infection should not be considered as
an exclusion criterion for this investigation. Doing so would underestimate the extent of infection in
the population. For individuals currently receiving medical care for COVID-19 infection, a family
member or proxy may be used to complete the questionnaire on his/her behalf.
2.4 Data collection
Each participant recruited into the investigation should be asked to complete a questionnaire which
covers demographic and exposure information. An example of an investigation questionnaire which
1
Riley S, Kwok KO, Wu KM et al. Epidemiological characteristics of 2009 (H1N1) pandemic influenza based on paired sera
from a longitudinal community cohort study. PLoS Med. 2011 Jun;8(6):e1000442
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