Understanding how COVID-19 spreads and how it can be contained
Accuracy of test
This is often used to describe both accuracy and reliability of a test. For COVID-19 this would mean how good a test is at confirming the presence or absence of an active or previous COVID-19 infection. No diagnostic test or antibody test is 100% accurate.
Aerosol
Very small respiratory droplets that can move through the air. They are involved in the transmission of some viruses.
Airborne transmission
Transmission occurring through very small virus-containing respiratory droplets produced by an infected individual. These can remain suspended in the air for hours and disperse further than 2 metres from the person producing them.
Antibody test
Detects antibodies to SARS-CoV-2 virus from a current or previous infection.
Antigen test
Detects viral material indicating a current infection. Tests for COVID-19 detect whether viral antigens found on the surface of SARS-CoV-2 are present in a sample.
Asymptomatic
Having an infection but not showing any symptoms.
Attack rate
The proportion of people who get infected after being exposed to the virus in a specific time window.
Case fatality ratio
The proportion of people with symptoms that die.
Contact
Person who has been close to someone who has tested positive for COVID-19. See UKHSA Guidance for more details.
Contact tracing
Identifying the source and contacts linked to a confirmed case of an infectious disease. Contacts can be classified as high risk, low risk or no risk and given advice on what to do. This approach is used as a public health measure to contain the spread of an infection.
- Forwards contact tracing – finding the people that the person who tested positive could have passed the virus to.
- Backwards contact tracing – finding the individual who gave the virus to the person who subsequently tested positive.
COVID-Status Certification
Documentation that indicates testing or vaccination data. See also Immunity passport and Vaccine passport.
Diagnostic test
A test that can confirm if someone has an active SARS-CoV-2 infection.
Doubling time
The time it takes for the number of infections to double.
Droplet transmission
Transmission occurring through large virus-containing respiratory droplets that are deposited close to an infected individual, with the risk that others nearby become infected.
Epidemiology
The study of what is causing a certain health outcome (diseases, environmental exposures, injuries), the distribution of diseases in different groups in the population, what causes them and changes over time. Knowledge from epidemiological research is used to design measures to control infectious disease.
Epidemiologist
Scientist studying epidemiology.
Excess mortality
Sometimes called excess deaths, this is the number of additional deaths in a time period that is higher than would usually be expected. For example, if there were normally 500 deaths in 1 week, but 750 were reported, this would equal 250 excess deaths.
False negative
An incorrect result. For example, when someone with a SARS-CoV-2 infection tests negative.
False positive
An incorrect result. For example, when someone who does not have a SARS-CoV-2 infection tests positive.
Flatten the curve
To reduce the peak rate of people being infected with the virus. ‘Curve’ refers to the number of new cases in a certain window of time. Reducing the peak will ensure that healthcare services are not overwhelmed.
Fomite
Object that can be contaminated with a pathogen and spread a disease. For example norovirus, often called the “winter vomiting bug”, can spread also through fomites.
Growth rate
Figure indicating how quickly the number of infections changes on a daily basis.
Immunity passport
Documentation that indicates an individual’s immune status. For COVID-19 this could be based on whether someone has been immunised or has antibodies because of a previous infection. There is insufficient evidence about the effectiveness of immunity passports. This is because having SARS-CoV-2 antibodies does not necessarily mean that someone is protected against a second infection (for instance, by a new variant). Antibody levels also decline over time following vaccination.
Incidence
The number of new cases of a disease in a population during a particular time period. Calculating incidence rates can indicate how quickly an infectious disease is occurring in a population.
Incubation period
The time between being infected and showing symptoms. Different variants can have different incubation periods. For the ‘original’ version of SARS-CoV-2 (identified in 2019), it can be as long as 14 days . For the Omicron variant , this is estimated to be around 3 days.
Infection fatality ratio
The proportion of infected people that die.
Index case
The patient in an outbreak of a disease who is first identified by health authorities.
LAMP test or RT-LAMP test (Reverse Transcription Loop-mediated isothermal AMPlification)
A scientific technique to detect and increase the amount of viral genetic material. Equipment using LAMP technology can be sited near to the person being tested and can give results in minutes instead of having to send samples for laboratory processing.
Lateral flow test
A type of molecular test to detect an active infection. The tests contain antibodies that bind to proteins (antigens) on the surface of the virus if it is present in a sample. A positive result is seen as a dark band or a fluorescent glow on the test kit, usually within minutes.
Mass spectrometry
A laboratory technique to identify specific molecules (such as viral proteins) in samples.
Mass testing
Using tests in a large sample of asymptomatic people to detect those who are currently infected.
Molecular test
A test that detects viral genetic material through PCR or newer laboratory techniques.
Morbidity
A term used to describe illness, injury or disability. Comorbidity or multimorbidity are sometimes used and refer to when someone has more than one condition at the same time.
Mortality
A term that means death. Mortality rates are an expression of the number of deaths for a given cause divided by the whole population.
Non-pharmaceutical interventions (NPIs)
Non-drug measures to limit the transmission of an infectious disease. These can be measures at the individual level such as physical distancing, the use of face masks and coverings, and improved hygiene measures. They can also be measures to constrain activities, such as the closures of various premises including sporting venues, pubs or shops.
PCR (Polymerase Chain Reaction) test
A specialised laboratory method used to increase the amount of DNA or RNA in a sample so there is enough to test it. PCR tests are used to detect RNA in samples from people to see if the samples contain SARS-CoV-2 virus.
Point-of-care test
A diagnostic test performed at or near to the person by a trained operator (like a urine dipstick to check for urinary tract infections).
Pooled testing
An approach to testing samples from a group of people using one test.
Prevalence
A measurement that expresses the proportion of people who have a disease at or during a given time period. Prevalence rates for disease are calculated by dividing the number of cases by the total number of people in the sample. They can be expressed as percentages or as cases per 100,000 people. It is often used alongside incidence, but they mean different things. While incidence counts only new cases in a given time period, prevalence counts both existing and new cases.
Primary case
The person who brings an infectious disease into a group of people, such as a country, city or workplace.
R (Reproduction Number)
A measure of how a disease spreads. The R number is the average number of people that one infected person will pass the virus onto. If R is more than 1 then an infection will spread in a population. Different SARS-CoV-2 variants can have different R values. For example, without any measures, R for the ‘original’ version of SARS-CoV-2 (identified in 2019) is estimated to be around 3, while R for the Omicron variant ( B.1.1.529) is estimated to be between 3 and 5.
Rapid test
While this refers to tests that can give a result in minutes rather than hours, the test may still require specialised equipment and/or trained operators.
Saliva test
A test that uses a saliva sample.
S gene drop-out
Term used to describe the failure of a PCR test targeting the SARS-CoV-2 gene of the spike protein. This phenomenon allowed the identification of the new SARS-CoV-2 variants. Also called S gene target failure.
Self-sampling
Describes when a person takes their own sample that is then sent elsewhere for processing and interpretation of results.
Self-isolation
The NHS website defines it as ‘when you do not leave your home because you have or might have coronavirus (COVID-19)’. Some use this term only when the person staying at home has tested positive for COVID-19.
Sensitivity
How well a test reports a positive result for people who have COVID-19.
Sequencing
A scientific technique to ‘read’ the genetic code of organisms. Both DNA and RNA can be sequenced.
Serial interval
The time between symptoms occurring in one person to symptoms appearing in the person they infect.
Specificity
How well a test reports a negative result for people who do not have COVID-19.
Super-spreader
Infected person who is highly contagious.
Swab test and self-swabbing
A type of self-sampling that uses a technique to take samples from the nose and throat for testing.
Symptomatic
Showing symptoms following an infection.
Transmissibility
The ability of a pathogen, like a virus, to spread from one person to another. See transmission.
Transmission
Process by which a pathogen, like a virus, spreads from one infected person to another.
Community transmission
When a disease is spreading in the community and the specific source is unknown (for instance, it cannot be linked to a traveller from abroad).
Quarantine
Period of self-isolation when returning from certain countries in order to reduce the risk of transmitting infectious diseases which might have been acquired during travel. It can be at home or in dedicated facilities. See the latest guidance in the House of Commons Library briefing Coronavirus: International Travel FAQs for England for the latest rules on quarantine. Some use the term quarantine to describe any circumstance where a person self-isolates as a result of confirmed or suspected exposure to a disease, even if the exposure did not take place in another country.
Vaccine passport
Documentation confirming that an individual has received a vaccine against COVID-19. See immunity passport.
Ventilation
The process of introducing fresh air into indoor spaces while removing stale air.
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