There are 1,564 confirmed cases of coronavirus in Ireland with nine deaths attributed to the disease.

Worldwide, there have been more than 447,000 confirmed cases and 20,599 deaths.

The epicentre of the disease has moved from China to Europe, and the World Health Organization has warned that the US could be next, after a "very large acceleration" in the number of cases there.

In Ireland, we've been living under a strange new reality since around St Patrick's Day, learning the language of social distancing, now physical distancing, not to mention how to cope with dramatically altered family lives.

With the help of countless charts, multiple memes and daily briefings, we're all (hopefully) becoming experts on coughing and sneezing etiquette (into your elbow like Batman, or even better, into a disposable tissue), proper handwashing and keeping our distance.

This last part is crucial because by keeping our distance from our friends, neighbours, colleagues and communities, we can help prevent the virus transmitting from person to person.

It’s also encouraging to hear that of the people testing positive for coronavirus in recent days, they’re showing fewer confirmed contacts than previously, down from 20 close contacts to just five. This means that people are taking the Government’s measures seriously, and are limiting their contacts to their own households, where possible.

But the disease is still spreading at various rates throughout the world.

Before we look at how coronavirus spreads, lets remember that 80% of people who do get the virus will have a mild illness and make a full recovery.

The World Health Organization says: "Most people infected with the Covid-19 virus will experience mild to moderate respiratory illness and recover without requiring special treatment. However, "older people, and those with underlying medical problems like cardiovascular disease, diabetes, chronic respiratory disease and cancer are more likely to develop serious illness." They're the people we want to do everything to protect.

Furthermore, the disease can be asymptomatic, meaning the infected person displays no symptoms at all, or in the early stages of infection. Those people can spread the disease unknowingly, particularly if they're not practising physical distancing.

In a paper published last week, scientists from Columbia University in New York examined early infections in China and found that high amounts of undocumented infection facilitated the rapid spread of coronavirus. This is where people had no symptoms or very mild symptoms and had not been tested, and went on to infect others unknowingly. The scientists estimated that "86% of all infections were undocumented prior to (the imposition of) 23 January 2020 travel restrictions." So, it’s key to remember that not just obviously sick people are a danger to others.

How does coronavirus spread?

According to the Health Service Executive's own advice, coronavirus is spread in sneeze or cough droplets. To infect you, it has to get from an infected person's nose or mouth into your eyes, nose or mouth. It’s not an airborne disease (like measles for example) but is transmitted through fluids. You can either inhale the droplets that a person coughs or sneezes, or you might even breathe in tiny droplets that someone emits when speaking, that’s why it's so important to stay around two metres or six feet away from people.

The WHO also points out that when an infected person coughs, sneezes or even breathes, tiny drops of saliva can land on objects and surfaces around the person. Other people then catch Covid-19 by touching these objects or surfaces, then touching their eyes, nose or mouth. This is why it's so important to wash your hands properly and often.

How long does the virus last on surfaces?

According to the WHO, it is not certain how long the virus that causes Covid-19 survives on surfaces, but it seems to behave like other coronaviruses. Studies suggest that coronaviruses (including preliminary information on the Covid-19 virus) may persist on surfaces for a few hours or up to several days. This may vary under different conditions (e.g. type of surface, temperature or humidity of the environment). If you think a surface may be infected, clean it with simple disinfectant to kill the virus and protect yourself and others. Clean your hands with an alcohol-based hand rub or wash them with soap and water. Avoid touching your eyes, mouth, or nose. Obviously, you can't go around disinfecting everything you touch, how would you go shopping for food, for example. So that’s why it's so important to wash your hands when you come home from essential trips outside.

RTÉ News spoke to Sam McConkey, infectious diseases specialist at the Royal College of Surgeons in Ireland, who answers some basic questions about coronavirus.

1. We know that the virus is spread from an infected person who coughs or sneezes, but what about their breath?

If someone is speaking loudly or animatedly - it's called forceful speaking - the vibrations of their vocal cords can create droplets in the air which can either fall to the ground or a nearby surface or they can be inhaled by a person nearby. That's why we’re all advised to stay two metres away from others outside our household. It’s not the case if you’re speaking softly and gently.

We’re all familiar with the image of the sun illuminating the drops when we cough and sneeze - that’s what you want to avoid doing and breathing in.

The droplets from a cough or sneeze are a bit bigger than the tiny airborne particles from speaking forcefully, and they fall down to the ground relatively quickly. The difficulty there is when our fingers pick up the virus particles and then we touch door handles or we touch our eyes, nose and mouth. Shaking hands is also a huge no-no for the same reason.

2. I read an article that said the saliva of Covid-19 patients can harbour half a trillion virus particles per teaspoon, and a cough aerosolises it into a diffuse mist. That sounds scary, is that accurate?

"Yes, the teaspoon analogy is ok - in infections with Hepatitis B, for example, a teaspoon of blood would have a similar amount of virus particles in it - it does sound like a lot of virus - but that's standard" (in infectious diseases).

Prof McConkey says it doesn’t take much for a small particle to get into your system, but we don’t yet know how much it takes to infect someone. Generally, one particle isn’t enough. Some of them are mutating so some of the particles are blanks – so if half a trillion virus particles are present in a teaspoon of saliva that doesn’t mean you could infect half a trillion people - it might take 100 or 1,000 particles to infect a person because some parts of the virus might not be able to infect people. But all in all, that figure of half a trillion particles in a teaspoon sounds about right.

3. How long does the virus last on a surface?

Prof McConkey says he read an article about the Diamond Princess cruise ship on which 800 of 3,000 passengers were infected with Covid-19. The Centers for Disease Control and Prevention in the US found that 17 days later there was still some virus detectable on surfaces. Now whether that was still infectious, we'll never know, but it still was present. It’s safe to say it survives from between one to multiple days.

Prof McConkey says we must continually go back to the basic reproductive rate of coronavirus.

The R0, as it's called, is estimated to be from 2.2 to 2.8 - so each individual case will infect that many secondary infections, i.e. one person infects around two people. Obviously, those people then infect four people, then eight people then 16, so it's an exponential epidemic. What we are trying to do is bring that rate to less than one. This would mean that the curve we’re all trying so hard to flatten goes down and the outbreak fizzles out.

"That doesn't mean the reproductive rate has to go to zero tomorrow, but if it’s reduced to less than one, the transmission slowly fizzles out - that’s what they’ve done in China, South Korea and Singapore - they’ve changed human contact enough to achieve an R0 of less than one."

Prof McConkey says if you can do that then the size of the area below the curve decreases - so you’re not just flattening the curve - you're decreasing the total number of people who will be infected. The worst case scenario is where we reach the peak of infection all at once, better is flattening the curve out so the daily number of infections is stretched out. But Prof McConkey says it’s even better still if we can all get so good at physical distancing that each case of Covid-19 infects less than one person.

4. I know the WHO advice is not to wear a mask, but should I cover my mouth with a scarf if I'm less than two metres away from someone outside the house?

Prof McConkey says people probably shouldn't be out if they’re worried about that. With our current guidelines, the advice is don’t go out where you’re closer than two metres or six feet to people.

5. Should I disinfect my groceries after I come home from food shopping?

"We all hope our groceries haven't been pawed over," Prof McConkey says, and he isn’t disinfecting his. "Obviously if someone sneezes on them that’s not great, but it gets very difficult if you have to disinfect everything that comes into the house" Again, the advice is wash your hands regularly and avoid touching your face.

Prof McConkey says what you eat goes into your stomach, and the virus is killed by your stomach acids, but he stresses that food isn't so much the issue in this case. "The quality of food in Ireland is generally very, very high - we're very lucky in that regard, food handlers generally have high levels of training and hygiene, so people needn’t worry so much about food."

He also points out that fear of food shortages is misplaced. "In Ireland we produce about 4-5 times more food than we consume. We'll have enough food - especially cheese, porridge, milk, beef - we'll be ok. There may be some changes to our food, but we’ll be ok."

Prof McConkey jokes that coronavirus won't cause a toilet roll or food problem at all. He says it is a huge problem but not of that kind.

6. Should I take my shoes off when I come into my house from outside?

If you sneeze, those droplets end up on the ground. At present we haven't been doing major disinfecting of our feet so it's a reasonable thing to consider. Droplets can end up on the floor, so it could be a good idea. When it comes to shoe hygiene - a disinfectant mat might be better, like what you see in a swimming pool. However, this is not something that the experts here have considered as essential. Prof McConkey says the foot and mouth disease approach (where people’s shoes were disinfected by mats doused in disinfectant) might be a good idea down the road. It's not unreasonable. However, he stresses that he’s not doing it himself at present.

He points out that while shoes may be a source of infection, a lot of the transmission in China was within households, 70-80%. It was that sort of close contact where people share cutlery, towels, beds. "It seems intimate contact was the problem, it wasn't a problem of brushing elbows at the traffic lights with strangers, it's a more intimate infection."

Prof McConkey says we do live in families for the most part - so that’s hard to eliminate - we are family units. The question is, can we keep each family unit separate from other family units as much as possible? That's why experts are advocating no unnecessary social contact.