By Siouxsie Wiles 14/05/2020 2


Today Aotearoa New Zealand wakes up in alert level two.

It’s no secret that I would have preferred for us to stay at level three for another week or so. That’s because I’m worried we don’t quite yet know how effective level three has been at keeping us on our path to eliminate Covid-19. But the government has had the unenviable task of balancing this risk with keeping the “team of five million” together. This has become especially important as protests against lockdowns and restrictions ripple troublingly around the world. So what are the risks at level two and how can we “play it safe”?

Just how many hidden transmission chains might there be in New Zealand?

Let’s start with the thing I’m worried about – the potential for unknown cases or chains of transmission to still be out there. As we’ve seen all around the world, if countries loosen their restrictions too soon or too quickly cases start to rise again. And because of the incubation period of the SARS-CoV-2 virus responsible and the resultant “lag”, it can take a couple of weeks before this becomes apparent. I don’t want that to happen here.

First for the really good news. As of now, we’ve had 1,147 confirmed and 300 probable cases of Covid-19. This means that when compared to many other countries in the world New Zealand has had relatively few cases. We’re what is known as a low prevalence country. Because we went hard and early, Covid-19 is not common in New Zealand. This is in complete contrast to many other countries that still have widespread transmission of the virus and a large number of new cases being reported each day, many they can’t trace back to other cases. Again, we know where almost all of our cases come from. Just 4% are listed as being of unknown source. These are the ones that concern me. Thankfully, they are a small number. But they could point to some unknown chains of transmission. So how can we flush them out?

One way is through widespread testing of people with no symptoms. If someone has or has had Covid-19 they should test positive for the genetic material of the virus for a few weeks, even if they are no longer unwell or infectious. According to the Ministry of Health’s website, as of May 9, 173,671 people in New Zealand had been tested for Covid-19. Remember, the test we are using here is only the one that looks for the genetic material of the virus. 1,147 confirmed cases from over 170,000 people tested means the vast majority of people presenting for testing didn’t have Covid-19. This isn’t because the test isn’t good enough. It’s very good. It’s because there isn’t much Covid-19 around here.

But, in the beginning, there was a very narrow case definition so our testing may well have missed some cases. As testing ramped up and the case definition was widened this should have happened less and less. Now any missed cases are more likely to reflect people who didn’t think their symptoms were worth getting tested, and it’s hard to put a number on that. But there’s been some random testing done at supermarkets which all came back negative so that’s comforting.

The Ministry of Health has released a document outlining their testing strategy for alert levels three and two. It’s good. It includes targeted testing of people with no symptoms if they work in health care and aged residential care facilities, quarantine hotels, or the tourism industry, as well as international travellers and airline crew, police, and migrant workers.

In summary, there may be some hidden chains of transmission out there, but they should be very few in number. Probably 10 at most. But recall Toby Morris’s animation, which shows how quickly transmission chains can end up growing out of control.

Cinemas vs churches: What are the risks at level two?

Before we get to how I think we should be playing it safe at alert level two, let’s quickly look at the risks around those hidden transmission chains. The first thing we know from the data so far is that people are infectious for a few days before they develop symptoms and for a few days after symptoms start. In other words, you can feel perfectly healthy and spread Covid-19.

The second thing we know is that what you are doing and how long you are doing it for matters. Lots of focus has been on coughing and sneezing being one way the virus spreads. There have been some very sad examples of people being deliberately coughed, sneezed, or spat on and then dying from Covid-19. So: no coughing, sneezing, or spitting on anyone, deliberately or otherwise. And if you do find yourself about to cough or sneeze, make sure you catch in a tissue or elbow. Using a high-speed camera, Dr Lydia Bourouiba recently showed that a vigorous sneeze can travel as far as seven or eight metres.

While touching contaminated objects like lift buttons and handrails is still considered a potential route for the transmission of Covid-19, it looks like talking, shouting, and singing are more important. Especially if people are indoors. Let me explain with some important examples. First up is this description of Covid-19 from a call centre in South Korea. Over the space of a week, 94 of the 216 people working on the same floor of a high-rise building came down with Covid-19. Most of them worked on the same side of the building.

You can see the floor’s seating plan in the diagram below. The desks of those who got Covid-19 are shown in blue. Despite using the lifts together, there were very few cases in people who worked on other floors of the building. But nearly half of those working in an environment with people constantly speaking on the phone caught Covid-19.

Another interesting cluster comes from an outbreak centred around a restaurant in China. In January, 10 people from three families who had eaten at the same air-conditioned restaurant came down with Covid-19. The index patient (A1), who wasn’t experiencing any symptoms at the time, went for lunch with three other members of their family. Two other families, B and C, sat at neighbouring tables a metre away. Families A and B overlapped in their time there by just under an hour, and families A and C overlapped by a little more than an hour. In this case the air-conditioning unit is thought to have pushed the virus to the downwind table. A couple of people on the upwind table also become infected. But no one sat at the tables on the other side of the room. Here we have a situation where people are likely chatting away as the virus heads off to other tables with the help of the air-con.

Noisy environments where people are crowded in together are becoming a bit of theme for Covid-19 transmission. Take meat processing plants. The current cluster in one in Melbourne is up to 85 cases, and there have been hundreds of workers affected in the US. What these and the previous examples show is that businesses need to be thinking very carefully about just how many people should be going back to work in indoor spaces, especially if they are noisy and crowded.

These examples also help explain why we can have 100 people apart from each other to watch a movie at the cinema but not to attend a church service. It’s not necessarily about the absolute number, it’s about what people are doing. In general, you need close contact with someone to spread or catch Covid-19. You don’t go to the movies and dash over to aisle J to hug someone. You sit with your friend and watch the film. Attending a church service is completely different. So, sitting in silence watching a movie? Low risk. At church and singing? High risk.

OK, but what about schools? I’ve covered the risks to children here. In general, the evidence to date suggests that children are less likely to come down with Covid-19 and less likely to transmit it. But this applies more to younger children than those in their late teens, so I’d be treating anyone 15 and older like adults who are going back to work.

So, given what we know about how Covid-19 spreads, here are my suggestions for how we can play it safe at alert level two.

Keep at home if sick

Staying home if you have any symptoms is really important for minimising the opportunities for Covid-19 to spread. But this is easier for some of us than others. If you are a business, what does your sick leave policy look like? Does it incentivise people to come in to work when unwell? What would happen if that person had Covid-19 and you ended up with your entire workforce in self-isolation?

Keep it quiet

All the evidence I’ve outlined here suggest that noisy environments, where people need to shout to be heard, are hot spots for the spread of Covid-19. This means we need to keep it quiet at least for the first few weeks of alert level two. If your workplace has music on in the background, keep it low so people can hear each other. I’m looking at you, restaurants and bars. If your workplace is noisy, are there ways to minimise this noise or reduce the number of people working at the same time?

Keeping it quiet also applies to activities like singing. Globally, there have been quite a few clusters centred around choirs, churches, and events with lots of singing and shouting. I think this is another activity that needs to be minimised especially in environments where there are other people not with your group.

Keep washing your hands

This one goes without saying. It is no less important to keep up with good hand hygiene now than when the pandemic started. There may still be droplets of the virus so keep washing your hands and don’t touch your face.

Keep your distance

Now’s still not the time to be shaking hands and kissing and doing all those things that bring your face and body in to contact with lots of other people. No matter how excited you are to see then after all these weeks. If you need some alternative greetings Toby’s got you covered.

Keep yourself covered

Let’s talk briefly about masks. Mass mask-wearing is something I’ve been reluctant to recommend for all sorts of reasons that I discussed here. The most important thing to remember about surgical and cloth masks is that they will likely stop you shedding some virus if you are infected, but they won’t protect you from becoming infected. So, as any one of us could be infectious for a few days before realising we have Covid-19, this is what I recommend for alert level two: that you wear a surgical or cloth mask when you are in badly ventilated spaces and/or are going to come in to close physical contact with people for more than a few minutes.

I’m thinking of scenarios like when using public transport, or if you work in a profession like hairdressing where you can’t maintain physical distance from your clients, or if you need to use a service that will put you in close contact with someone for more than a few minutes. What’s important about masks is that you know how to wear them and dispose of them properly. Check out this article here.

Keep notes

As we move into alert level two, what we need to remember is that we are going to be relying on our health service’s test, trace, and isolate strategy to stamp out any transmission chains that do pop up. So, keep track of where you have been and who with and the minute you experience any of the symptoms that could be Covid-19, call Healthline to organise a test.

The post was originally published on The Spinoff.


2 Responses to “Simple rules to play it safe at alert level two”

  • The best part about generic symptom lists, is that they tell me I have been suffering from Covid-19 for at least the last 10 years.

  • The government has rejected call from a leading epidemiologist that mask wearing be made mandatory on public transport.

    Scientific American is a globally respected popular science journal. What they have to say on this issue is important.

     ……Crowded areas such as bars, restaurants and subway trains could all be risky—especially if people are asymptomatic and spend long periods of time in such areas. Precautions could include better ventilation, regular cleaning and mask wearing.

    Cowling co-authored a study, published in early April in Nature Medicine, of patients with respiratory infections at an outpatient clinic in Hong Kong between 2013 and 2016. This research detected RNA from seasonal coronaviruses—the kind that cause colds, not COVID-19—as well as seasonal influenza viruses and rhinoviruses, in both droplets and aerosols in the patients’ exhaled breath. The paper, led by Nancy Leung, an assistant professor at the University of Hong Kong’s school of public health, found that wearing surgical masks reduced the amounts of influenza RNA in droplets and of seasonal coronavirus RNA in aerosols.

    Although the study did not look at COVID-19 specifically, the findings support mask wearing as an effective way to limit transmission of the virus from an infected person—known in medical parlance as source control. There is not much evidence that masks convey protection to healthy people, although it is possible (and may depend on the type of mask). Given the prevalence of asymptomatic infection with COVID-19, however, there is some justification for universal mask wearing to prevent those who do not know they are sick from infecting others. In Hong Kong, which has kept its outbreak relatively under control, masks are worn by the vast majority of the population, Cowling says.

    https://www.scientificamerican.com/article/how-coronavirus-spreads-through-the-air-what-we-know-so-far1/?utm_source=newsletter&utm_medium=email&utm_campaign=week-in-science&utm_content=link&utm_term=2020-05-15_featured-this-week&spMailingID=65261882&spUserID=MzA0NTQ4NDI1MzE5S0&spJobID=1882303173&spReportId=MTg4MjMwMzE3MwS2