How CBS compiles mortality figures in times of corona

04/08/2020 15:00 / Author: Corporate communication

Statistics Netherlands (CBS) is responsible for compiling statistics on all deceased persons in the Netherlands, along with their cause of death. CBS has published figures on this subject since 1899, when statistical records were first kept. The COVID-19 outbreak presented CBS with a challenge that had not arisen since the Spanish flu: how do you take stock of the course of a pandemic caused by a novel virus? Excess mortality could be calculated fairly quickly. However, compiling causes of death statistics involves a complex process. On 31 July, CBS published its provisional cause-of-death figures for the first four months of 2020. Eva Krpelanová, medical officer at CBS and pathologist, gives us the inside story on how the causes of death statistic is being compiled during the coronavirus crisis.

How could excess mortality be calculated quickly?

‘When a person dies, a post mortem is carried out by the attending physician or a locum or – if a non-natural death cause is suspected – by a forensic physician. The physician in question fills in two forms: a death certificate and a cause of death form. The undertaker then makes sure that these forms are submitted to the municipality where the person died. The municipality only processes the death certificate, which contains personal data, and registers that the person in question has died. It then delivers this data to CBS in encrypted form, making sure the necessary safeguards are in place to ensure privacy. This enables CBS to obtain a reasonably quick overview of the number of people who have died and this provides a basis for calculating excess mortality.’

So processing causes of death is more complex?

‘That’s right. There are a number of reasons for this. The first is procedural: municipalities do not process cause of death forms. The law stipulates that this must be done by CBS. Municipalities put a deed number and their municipal code on the envelope of the cause of death form, and these correspond with the death certificate of the person in question. They send these envelopes to CBS once a month. We then process the cause of death forms manually. The numbers and codes on the envelopes enable CBS to link the cause of death forms to the death certificates supplied by the municipalities while guaranteeing the privacy of the individuals concerned. The name of the deceased person does not appear on these forms.’

Why is the cause of death submitted in writing?

‘The Burial and Cremation Act stipulates that cause of death forms must be submitted in writing to CBS. An amendment to this law is currently under way, which will make digital delivery possible. As part of this change, a number of pilot projects are taking place, involving general practitioners, hospitals and forensic physicians among others. Physicians will soon be able to send the completed form digitally and directly to CBS. However, this legislative amendment has yet to be implemented and until it is, written submission outside the pilot projects is still required by law.’

What makes the classification of causes of death so complex?

‘CBS enters all the data on the cause of death form into its system manually. This includes both non-medical data – such as municipality, age and gender – and medical data, such as illnesses or medical conditions. CBS staff then code the causes of death entered. On the cause of death form, the examining physician fills in the chain of causes that led to the person’s death. In the case of lung cancer, for example, metastases may have spread to the liver, causing bleeding which ultimately resulted in the person’s death. In that case, internal bleeding is the direct cause of death, but lung cancer is the underlying cause of death. It is this underlying cause of death that is included in the statistics. CBS codes the causes of death according to the classification system drawn up by the World Health Organization (WHO). Using international statistical encoding software, CBS is able to automatically encode approximately 60 percent of all cause of death forms. The remaining 40 percent have to be read manually and coded by specialised coders. In some cases, the coders may need to contact the physician who filled in the form to obtain a clear or complete picture of the necessary information.’

How is COVID-19 encoded?

‘The WHO issued a classification code for COVID-19 in January of this year. This was intended for cases in which infection had been established. But because this is a new coronavirus, not all of the symptoms were known and not all patients were tested. This meant that in some fatal cases there was a strong suspicion of COVID-19 infection that had not been verified by lab tests. At the end of March, the WHO therefore introduced a new classification code for suspected COVID-19 infection. This enabled a distinction to be made between established and suspected contamination. This classification code was applied retroactively dating back to 1 January 2020.’

How has the pandemic affected cause of death statistics?

‘The pandemic put enormous pressure on the health care sector and filling in forms understandably became less of a priority. Due to the excess mortality, more forms than usual had to be processed. The municipalities were faced with the same problem, at a time when their own working processes were being seriously disrupted by the lockdown. As a result, CBS was receiving more cause of death forms and more sporadically than usual – all perfectly understandable given the circumstances. Because COVID-19 is a new virus, we didn’t know how physicians would fill in the forms. More forms therefore had to be coded manually, while CBS was also in lockdown and directly affected by the pandemic. CBS has been doing everything in its power to process the cause of death forms as quickly as possible. A lot of people have worked very, very hard to make that happen.’

The published figures have been labelled ‘provisional’. Why is that?

‘Each quarter, CBS publishes the provisional figures on causes of death. This means that not all forms have yet been received and processed, but at least 95 percent have – and that’s our threshold for publication. The final figures are not published until the following year. On 1 July, for example, CBS published the cause of death figures for 2019. Given the huge impact of the COVID crisis, there is an urgent and very understandable demand throughout society for up-to-date figures on the causes of death. It’s important to make it clear that causes of death statistics are not used in policy-making decisions during the pandemic. These statistics exist to provide a picture of long-term developments.
Because the peak of the pandemic was in April, CBS set itself the task of publishing not only the first quarter, but also the figures for April. Here, too, we applied the threshold of 95 percent of all forms and we made sure that data from all municipalities were present. Because CBS is able to make the link with the municipal data on deceased persons, we know exactly how many causes of death have been processed.’

What can this data be used for?

‘The causes of death statistic has multiple applications. The data is used nationally and internationally to monitor and analyse statistical trends in causes of death. Universities, epidemiologists and medical associations use the data to conduct further research. The data can also be used for combined analyses, for example in relation to socioeconomic status or underlying health conditions. In the case of COVID-19, the statistic also supplements the data from the National Institute for Public Health and the Environment (RIVM), Municipal Health Services and GP associations.