Most of us fear the worst when we sit on a crowded plane or train next to someone who has a bad cough, or when we hear that the friend we had drinks with last night has tested positive for Covid, or that your child's school friend threw up in the classroom I wonder if or just when we will have to deal with the same illness.
With the winter flu and sickness sickness season already in full swing, the number of Covid infections still circulating – and now news of measles outbreaks – it seems inevitable that you will come down with one of these illnesses.
Or we come across a mistake and try to figure out who was to blame – a kind of blame game that is common both at home and at work. But not all infections spread as easily as others.
This depends on the interaction of various factors, including how robust the infected person's immune system is and the incubation period, i.e. the number of days that pass after infection with the virus until symptoms appear.
You catch a cold or flu by inhaling particles of the virus, usually in a droplet of mucus from an infected person, through coughing or sneezing – but also by touching contaminated surfaces, says Professor Eccles
But one of the most important factors is the pathogen's reproduction rate (or R rate), a measure of how contagious it is based on the average number of secondary infections a person causes.
An R rate of 1 means that, on average, each infected person infects one other person.
Interestingly, two of the most contagious diseases of all are measles (caused by a virus, morbillivirus) and whooping cough (caused by a bacteria, Bordetella pertussis), with the highest R rates – 15-20 and 15-17, respectively. This means that one infected person can infect up to 20 others with measles and up to 17 with whooping cough.
For this reason, the current measles outbreaks in Birmingham and London are of great concern, as nine out of ten people who have been in a room with an infected person will become infected with measles if not through a previous infection or vaccination are immune.
At the other end of the spectrum is tuberculosis (TB), one of the deadliest infectious diseases, whose R rate is below 1 in the UK (although it is higher in other parts of the world where it is more common), meaning it is is an infection It is unlikely that one person will infect someone else – becoming infected requires prolonged close contact, not just sitting next to someone on a bus.
Bedbugs that spread well have certain characteristics that help them do so. For example, the bacteria that causes whooping cough causes coughing for six to 10 weeks to maximize its potential to spread.
Each insect's incubation period is also unique – for some infections (such as a cold), you will notice symptoms within a few days of exposure, but for others it may take several weeks for symptoms to appear. For example, measles and chickenpox (caused by the varicella-zoster virus) have an incubation period of up to three weeks.
Most viruses infect us using the same mechanism. Whether they enter via the nose, orally or through the skin, they enter cells and hijack the machinery to support replication. Then they break out and move around to infect more cells
Whether or not an infected person is contagious during the incubation period depends on the type of infection. For measles and chickenpox, for example, the person may not be aware that they are infected and may appear to spread the viral droplets to others weeks before their own symptoms.
“It's not clear why some have a longer incubation period than others, but it's probably because they evade the immune system,” says Ron Eccles, emeritus professor and former director of the Common Cold Center at Cardiff University.
“A number of factors influence whether or not you catch an infection, including how much of the virus the person you are in contact with is 'shedding' at that moment; whether you are in an enclosed space or not; the temperature and humidity of the environment (e.g. cold viruses survive better in humid conditions) – and whether you are immune, as well as your age, general health and genes.
Most viruses infect us using the same mechanism. Whether they enter via the nose, orally or through the skin, they enter cells and hijack the machinery to support replication. Then they break out and move around to infect more cells, explains Professor Eccles.
READ MORE: My 11-month-old son was hospitalized with measles – I want the MMR vaccine to be offered before he turns one
“In this stage, your immune system begins to recognize the virus.” In the first stage, the white blood cells release peroxide chemicals that can damage or absorb the pathogens. However, after five to ten days, they begin producing virus-specific antibodies that rid the body of the infection.
“This reaction leads to symptoms such as shivering and feeling hot: these are signs that the body is trying to fight off the infection,” he says.
Genetic factors can also play a role in whether you catch an infection and develop symptoms, adds Professor Sheena Cruickshank, an immunologist at the University of Manchester.
“In studies where people are exposed to common viruses like colds under laboratory conditions, some people do not become infected with the viruses, while others become seriously ill,” she says. “This is due to the efficiency of your immune system and our genetics.”
“In addition, the more immune you are to the pathogen, the less likely you are to be a good host for the virus to multiply and spread to other people – which is an argument in favor of vaccination; “You not only protect yourself, but also others.”
We asked leading experts how infectious some of the most common infections are and how best to protect yourself.
MEASLES
WHAT IS IT: Caused by a virus, morbillivirus, it is very contagious and initially causes flu-like symptoms and then a red, blotchy rash on the skin.
SPREAD: The R rate (how contagious it is based on the average number of secondary infections a person causes) is 15 to 20.
The measles virus spreads easily through droplets from coughs and sneezes (unlike chickenpox, which can also enter skin particles, forming a fine dust that is spread into the atmosphere).
The measles virus is airborne and can become infected even two hours after an infected person leaves the room.
INCUBATION PERIOD (how long it takes for symptoms to appear after an infection): Seven to 18 days. On average, symptoms such as cough, fever and runny or red eyes appear after ten to twelve days – these symptoms can be very similar to a cold.
A rash appears three to five days later. “The measles rash usually starts behind the ears and spreads along the hairline and across the body,” explains Dr. Samira Neshat, consultant pediatrician in intensive care at the Royal London Hospital in London and the private HCA The Portland Hospital for Women and Children.
This delayed response is because immune cells need time to bind to the virus and get stuck in the skin – “then spots appear,” says Professor Eccles.
How long are you contagious? You can shed the virus and infect others from four days before the rash begins to four days after the rash appears.
Dr. Neshat says measles can be a frightening disease if you're not vaccinated or don't have immunity, because 30 percent of people can develop complications like severe diarrhea and a middle ear infection – and more serious complications like encephalitis (an infection of the brain). , which can be fatal. “It is so important that you get your child vaccinated as a full course of two doses is 97 percent effective.”
cold and flu
WHAT IS IT: There are hundreds of different cold viruses – about 200, half of which are rhinoviruses (“rhino” means the nose and are transmitted through respiratory droplets). There are more than 60 flu viruses – the four main strains are A, B, C and D; Seasonal flu is caused by A and B strains that mutate every year.
DISTRIBUTION: The R value for both is 1 to 2 but may vary.
Cold and flu viruses spread easily; You will probably have more colds in your life than any other illness. “This is because colds generally cause mild illness and people go to work and school and spread the viruses further,” says Professor Eccles. “Flu viruses are slightly more contagious because there are new ones every year, so you are not immune to them and therefore they have a greater chance of spreading successfully.”
“You catch a cold or flu by inhaling particles of the virus, usually in a droplet of mucus from an infected person, through coughing or sneezing – but also by touching surfaces that have been contaminated with these droplets (the viruses can last for some time survive). hours outside the body) and then touching the mouth, nose or eyes,” adds Professor Eccles.
“The viruses can attach to cells in the back of the nose, and that is often where the first signs of infection appear – for example, a sore throat or tickling.”
“While flu viruses are slightly more contagious than cold viruses, the problem with colds is that they cause relatively mild illness and don't produce a strong antibody response, so you can get infected again with the same virus after a few weeks.”
INCUBATION PERIOD: 12 hours to three days after infection with one of the two types of infection.
How long are you contagious? Up to 14 days after symptoms start or even 1-2 days before. You are most contagious in the first three days after symptoms begin, then the risk of infection gradually decreases as your immune system responds.
“Technically you can be infected without having symptoms and still spread it – but that’s unusual,” says Professor Eccles.
NOROVIRUS
WHAT IS IT: This is a highly contagious virus, also known as winter vomiting virus, that causes vomiting and diarrhea. It can spread quickly in households, hospital wards, nursing homes and schools.
DISTRIBUTION: The R-value is 1.1 to 7.2.
It takes fewer than 100 particles to make you sick, and people excrete billions in their stool and vomit. Because it is airborne, you can become infected through inhalation, but also through infected food and water, and contaminated surfaces (it can survive on hard surfaces for 12 hours, and on soft surfaces like carpets for up to 12 days).
INCUBATION PERIOD: 12 to 48 hours.
How long are you contagious? According to the NHS, you will still be contagious for 48 hours after your symptoms have subsided. However, some studies suggest that you can still spread it even after several weeks.
The reason norovirus is so contagious is because it has so many routes of transmission and remains outside the body for some time, says Professor Cruickshank.
“It can spread easily because sometimes people don't realize it's in the air and if you don't cover the toilet cover, for example, virus particles are in the air and can be inhaled or contaminate nearby surfaces.”
“It also mutates every year and some strains are very good at evading the immune system, have higher replication rates and are better at penetrating cells.”
COVID-19
WHAT IS IT: An infectious disease caused by the SARS-Cov-2 virus. It can attach to cells throughout the body and cause a variety of symptoms, from persistent coughing and shortness of breath to intestinal problems such as diarrhea and vomiting.
Although Covid-19 spreads easily, Professor Kucharski says: “Immunity in the population is now much greater due to vaccination and previous exposure to the virus, so the disease will generally be milder than in 2020.”
DISTRIBUTION: The R-value is 1.9 to 3.9.
Like many viruses, Covid spreads easily via tiny droplets from coughs and sneezes – and to a lesser extent by touching an infected surface (the virus loses its infectiousness on surfaces within six to 12 hours, says Professor Eccles).
Although primarily a respiratory infection, this virus has the ability to attach to receptors throughout the body.
Adam Kucharski, professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine, says the reason Covid spread so effectively was because people were contagious before they developed symptoms – and that's still the case .
“From a virus transmission perspective, this has a positive effect on the virus because there are a number of people who are shedding large amounts of the virus without knowing that they are infectious.”
“People may be concerned if they hear someone with a persistent cough in a public space, but by that time they may have already reached the end of their infection and the amount of virus coming out – if any – is lower.”
He adds that if one person is infected, the real risk of someone else in their household becoming infected is about 25 percent.
INCUBATION PERIOD: 2 to 14 days. “People now appear to be developing symptoms much more quickly, in some cases within two days,” says Professor Eccles.
How long are you contagious? This depends on the quality and quantity of your immunity (for example from a vaccination or a previous infection) – some people are no longer contagious after five days, others can be contagious for up to ten days, according to the NHS.
Danny Altmann, professor of infectious diseases at Imperial College London, says the Covid virus has changed since the pandemic began four years ago. New variants can spread better between cells in the body and evade our antibodies better.
The latest Covid variant JN.1 is “significantly better” than the variant from six months ago in terms of its ability to enter cells and the speed of spread between them, he adds.
Although it spreads easily, Professor Kucharski says: “The population's immunity to Covid is now much greater due to vaccination and previous exposure to the virus, so the disease will generally be milder than in 2020.”
WHOOPING COUGH
WHAT IS IT: Caused by the bacterium Bordetella pertussis, it affects the lungs and respiratory tract, causing a cough that can last up to ten weeks.
DISTRIBUTION: R rate is 15 to 17.
The bacteria reside in the cilia hairs in the nose and are easily spread through the air through sneezing and coughing.
INCUBATION PERIOD: 5 to 10 days.
How long are you contagious? Cold-like symptoms appear after the incubation period. Two weeks later, these may worsen into coughing fits (followed by a wheezing sound as you gasp for air).
You are contagious from six days after infection, when flu/cold-like symptoms begin, until three weeks after coughing attacks begin. You may have symptoms for up to ten weeks but may not still be contagious. Treatment includes antibiotics and earlier treatment can reduce the severity of coughing attacks.
Dr. Neshat says, “It's not always obvious whether someone has whooping cough in the early stages.” It seems like it's nothing more than a cold. The main difference is that babies can experience apneas, i.e. life-threatening pauses in breathing. Babies in the UK are routinely vaccinated against whooping cough at eight weeks of age and this is the best protection.”