The graphs below appeared in ESR’s COVID-19 Intelligence Summary for April 20 and were referenced by Director-General of Health Ashley Bloomfield at the media stand-up (21 April) to explain why New Zealand’s COVID-19 testing numbers have dropped during level 4 lockdown.
The Figure above shows that daily national rates of calls to Healthline for advice on influenza-like illness (ILI) by the general public have followed a similar pattern to the national notifications of COVID-19. Rates of ILI-related calls to Healthline increased as national COVID-19 case notifications increased, peaking on the week New Zealand moved to alert levels 3 and 4. Daily call rates significantly decreased following the lockdown. This trend can be seen in nearly all major population centres when looking at rates at the District Health Board level (DHB) as shown in the Figure below.
Caution is advised when interpreting Healthline ILI-related call trends as these are affected by a number of factors including the current COVID-19 response (i.e. rates of calls may not truly reflect levels of community illness activity because rates of calls may be affected by other factors).
The Figure above shows the national weekly incidence rates of General Practice visits for influenza-like illness (ILI) reported through HealthStat (blue), relative to the historical mean (2016-2019) (red). The current national weekly incidence of GP ILI visits is within expected historic baseline levels. However, it is important to note that changes to how patients present with influenza-like illness to healthcare providers as a result of the COVID-19 response can limit the interpretation of current trends. HealthStat practice participation is being expanded by the Ministry of Health.
The Figure below shows weekly District Health Board (DHB) rates of GP visits for ILI detected through HealthStat. Rates are at expected inter-seasonal weekly levels among DHBs. Spikes in weekly incidence should be interpreted with caution in less populous DHBs where HealthStat practice coverage has been lower and where a small increase in presentations can have a disproportionate impact on incidence rates.