Director of health Ashley Bloomfield, who, on most days, reads the numbers that will define how the rest of this year plays out (Illustration: Simon Chesterman)

Covid-19: New Zealand cases mapped and charted, April 1

The third in our new series of charts, graphics and data visualisations by Chris McDowall, covering the Covid-19 epidemic within New Zealand. We’ll publish the latest set each day on The Spinoff.

This work is entirely funded by the generosity of The Spinoff Members

Information about confirmed and probable cases of Covid-19 in New Zealand is changing rapidly. These posts collate the most recent statistics and presents them as charts and maps. The Ministry of Health typically publishes data updates in the early afternoon, which describe the situation at 9am on the day of release. The Spinoff will release a new version of these data visualisations each day in the immediate aftermath of the Ministry of Health updates. They will evolve and refine over the coming days and weeks.

These data visualisations are interactive – ‘mouse over’ each graph for more detail.

Note for users of The Spinoff App: the charts are not supported within the app yet. Please click here to launch in a separate browser window.

This afternoon the director-general of health announced that the number of Covid-19 cases stands at 708 (647 confirmed cases and 61 probable). Eighty-two people have recovered, an increase of eight over the last 24 hours. The ministry also reported that they averaged 1,843 Covid-19 lab tests per day during the week ending March 31. A total of 23,481 lab tests have been conducted to date.

The Ministry of Health revised their classification for what constitutes a cluster. Previously groups of three or four people were included in the cluster counts. From today clusters are groups of more than 10 cases. Under the new definition, seven clusters being investigated by public health officials. These figures include confirmed and probable cases.

Two clusters registered significant increases in the number of confirmed and active cases over the last 24 hours. The cluster around a wedding in Southland DHB jumped from eight cases under investigation yesterday to 22 today — an increase of 14 cases. The Matamata cluster, which is focused on a bar, jumped by nine cases overnight (from 23 to 32 cases).

This symbol map shows confirmed and probable Covid-19 cases arranged by district health board. The highest counts of confirmed and probable Covid-19 are still Southern, Auckland, Waitematā and Waikato DHBs.

A few people have asked me to include rates noting the percentage of people who have contracted the disease in each district health board. I reflected on this and consulted some statistics colleagues. We were in agreement that, as things currently stand, per-capita numbers are probably inappropriate.

  • The geographic distribution of cases within each DHB is uneven – consider the clusters – so cases per capita gives a false impression of the risk of catching Covid-19 in different areas
  • The denominator is not really relevant from the point of view of disease transmission, because we are so far from saturation. Any cluster, even one in West Coast or Tairāwhiti, could grow by orders of magnitude before starting to run out of hosts.

However, I will add district health board population counts to the map mouseover. Thanks to Thomas Lumley, Aaron Schiff, Harkanwal Singh and David O’Sullivan for the quick feedback.

This bar chart displays confirmed and probable cases by the date reported. If you compare the chart carefully with the previous day, you will see a slight increase in the number of confirmed cases for each day. This is due to the lag between testing and reporting. Sometime in the coming week I will produce an animation to show this effect in play.

Today the prime minister notes people in their 20s as the age group with the highest number of Covid-19.

“They are our vector for transmission, so I need everyone to take this seriously. They are the ones that pass it on.”

The number of people in this age group who are confirmed to have the virus increased from 158 to 167 overnight. The number of probable cases for people in their 20s rose from 11 to 16.


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