1) Asymptomatic carriers are a major source of COVID-19 infections, accounting for up to 40% of cases. 2) Rapid antigen tests are less sensitive than PCR tests and more likely to produce false negatives, especially for those without symptoms or with low viral loads. 3) While no single measure provides complete protection from COVID-19, combining masking, physical distancing, handwashing, and avoiding crowds significantly reduces infection risk.

1. COVID-19
GRAPHICAL ABSTRACT

2. Infectious dose
• Varies from person to person
• No firm data yet about what is the
typical dose might be

3. Exposure and
incubation

4. Asymptomatic are the major source
• Up to 40 percent of infections might lack symptoms, although some
estimates have been even higher

5. Charting a Coronavirus Infection

6. Symptoms and recovery

7. Testing for the virus

8. Rapid antigen tests
• Worse at picking up on low viral loads and very recent infections
• more often produce false negatives or false positives
• Some experts argue that true positives from rapid tests might
coincide with the period in which people are most contagious,
although this has not yet been confirmed
• Use on individuals who don’t feel ill is considered off-label, and
negative results from such tests can’t rule out an infection or
contagiousness.

9. P.C.R. (polymerase chain reaction)
• can detect very small amounts of the virus
• usually takes several hours to run on sophisticated, expensive
machines
• Can also pick up harmless bits of the virus that linger in the body after
symptoms have resolved, and perhaps after a person stops being
contagious

10. Serology test: looks for the antibodies
• produced by the body in response to an invading pathogen, starting
about a week or so into an infection, and can persist in the blood for
months
• Not considered to be a reliable way to determine whether a person is
harboring the coronavirus

11. Preventing infection
• People who feel healthy also disseminate infection
• Avoiding crowded spaces rapidly ratchets down risk
• No single tactic can confer complete protection
• Combine mask-wearing, physical distancing, handwashing
• Avoiding crowded places rapidly ratchets down risk

12. Mask
• Masks and face coverings that
swaddle the nose and mouth
• Can block much of transmission
and seem especially effective at
waylaying outbound virus from an
infected individual
• Masks can thwart some
percentage of inbound pathogens
,in case of reuse ,look for
• Mask wearer are not impervious to
infection

13. Preventing
infection

14. Conclusion
• The Centers for Disease Control and
Prevention note that people with Covid-19
are unlikely to be infectious for more than
10 to 20 days after their symptoms start