Coronavirus disease (COVID-19) technical guidance by WHO Household transmission investigation protocol | Page 17

virological testing, regardless of symptoms, and at the Day 28 visit, a serum sample (and other
potentially relevant specimens) could be collected from all household contacts – see Fig. 1.
Other specimens (oral fluid, urine, faeces, etc.), as described for confirmed cases, may be collected.
2.5.1.3 Note on serology
Paired clotted blood samples should be taken for serology and handled and separated correctly by
the laboratory. Paired serological samples cases are needed to aid the development of serological
testing, in order to determine an accurate SIR and the proportion of infections that are
asymptomatic.
Serum samples should be taken from all confirmed COVID-19 cases, and from household contacts,
regardless of symptoms.
 An acute baseline clotted blood sample should be taken as soon as possible, and ideally no
later than 7 days after symptom onset (for cases) and no later than 7 days after exposure
with the confirmed cases (for household contacts).
 A follow-up (or convalescent) clotted blood sample should be taken:
- at least 14 days after the baseline sample; or
- (for a case) 28 days after symptom onset if an acute sample couldn’t be taken when
the case was symptomatic; or
- (for a household contact) 28 days after the last exposure if an acute sample wasn’t
taken.
2.5.2 Specimen transport
All those involved in collecting and transporting specimens should be trained in safe handling
practices and spill decontamination procedures. For details regarding the transport of samples
collected and infection control advice, please refer to the case management algorithm and
laboratory guidance in the country or WHO laboratory guidance, available on the WHO website (8).
For each biological sample collected, the time of collection, the conditions for transportation and the
time of arrival at the study laboratory will be recorded. Specimens should reach the laboratory as
soon as possible after collection. If the specimen is not likely to reach the laboratory within 72 hours,
it should be frozen, preferably at –80°C, and shipped on dry ice. It is, however, important to avoid
repeated freezing and thawing of specimens. The storage of respiratory and serum specimens in
domestic frost-free freezers should be avoided, owing to their wide temperature fluctuations. Serum
should be separated from whole blood and can be stored and shipped at 4 °C or frozen to –20 °C or
lower and shipped on dry ice.
Transport of specimens within national borders should comply with applicable national regulations.
International transport of specimens should follow applicable international regulations as described
in the WHO Guidance on regulations for the transport of infectious substances 2019–2020 (20).
2.6 Ethical considerations
Ethical requirements will vary by country. In some countries, this investigation may fall under public
health surveillance (emergency response) acts and may not require ethical approval from an
institutional review board.
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