How many people actually develop sepsis in Norway?

Sepsis is a serious illness that affects many people. But exactly how many is unknown and the estimates vary widely. Why is this so difficult to find out?

Diagnosis coding practices are influenced by finances
The incidence of sepsis is often based on administrative data from hospitals in the form of ICD codes (ICD-9 and 10). Coding practices vary between departments and hospitals. The figures are thus influenced by the quality of documentation and diagnosis in individual departments. In addition, financial incentives play a role in what code is used.

In Sweden, only 18% of all patients with sepsis received an explicit sepsis code. In order to  capture more patients with real sepsis, several attempts have been made to create combination diagnostic codes (Angus, Flaatten, Martin). Today's coding practices do not provide a clear count of how many people die from sepsis in Norway.

The World Health Organization and the Global Sepsis Alliance have both pointed out that a standardized coding practice is a good tool for obtaining an accurate count of the number of sepsis patients.

"We need to recognize that Norwegian estimates of the total incidence of sepsis are probably too low."

Sepsis outside the intensive care unit
Only the sickest patients with organ failure are admitted to the intensive care unit (ICU). That means that the majority of patients with sepsis are treated outside ICUs. Intensive care records can thus not be used to tell us anything about the totalincidence of sepsis. On the other hand, these records cover the very sickest patients and give us important information on the incidence and mortality rate of septic shock.

Unfortunately, it also turns out that that the way ICD codes are applied in the intensive care units does not adequately cover sepsis, either. Of 9271 patients with sepsis in the Swedish Intensive Care Registry, 55.4% were discharged without any ICD code combinations for sepsis. The diagnostic combination codes developed by Flaatten and used in the Swedish intensive care registry identified the greatest number, specifically 39.8%, of patients with sepsis. This means that even for patients in intensive care units who are critically ill and receive organ support therapy, the coding practice for sepsis is not good enough.
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Figures from the Norwegian Intensive Care Registry show that in 2017 and 2018, a total of 2886 patients were registered with sepsis as the main diagnosis. The incidence of intensive care sepsis is thus approximately 33/100 000. It is unknown how many of these patients had ICD codes for sepsis, nor do we know how many intensive care patients with other main diagnoses also had sepsis.

What about the total incidence of sepsis?
The most important question we have to ask is: how many people actually develop sepsis each year?

Few countries have data on this. Most materials are retrospective and the numbers vary widely, probably because the researchers have used different methods. A study from Denmark found an incidence of community-acquired sepsis of 457/100 000 in the population over 15 years. A study from Sweden included everyone over the age of 18 with "severe sepsis" according to the sepsis-2 definition in two regions and reported an incidence of 687/100 000. Lars Ljungstrøm and colleagues recently published a prospective registration of community-acquired sepsis admitted to hospital. They found an incidence of "severe sepsis" of 276/100 000; sepsis according to the sepsis-3 criteria of 838/100 000; and bacterial bacteria 203/100 000. A large Chinese study found an incidence of 236/100 000 in hospitalized patients over 18 years.

These studies illustrate how difficult it is to determine the incidence of sepsis, even within one country.
Unfortunately, there are few population-based studies on the incidence of sepsis in Norway. One study found an incidence of hospitalized sepsis in Norway in 2011-12 of 140/100 000. The same study found a hospital mortality rate of 26.4%. This corresponds to 7000 cases and 1850 deaths a year. In this study, the researchers used retrospective data and the method of combining ICD codes for sepsis with ICD codes for organ dysfunction. As mentioned above, this method captures 39.8% of patients with sepsis.

Population-based studies from the Faroe Islands and the United States have reported incidence rates of 644/100 000 and 580/100 000, respectively. Along with the above-mentioned studies that report incidences from 140-687 per 100 000, these numbers underscore the uncertainty in the figures.

Using only the Norwegian data results in 7000 cases of sepsis a year and 1850 deaths. If the highest figures from Swedish and Danish studies are used, we get an annual incidence of 42 000 cases . Such a huge difference between Norwegian and Swedish conditions seems unlikely. We need to acknowledge that Norwegian estimates of total incidence of sepsis are probably too low. A possible estimate would be around 20 000 cases a year with an annual mortality rate of 3000 to 6000.
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Currently, doctors, researchers and politicians have to deal with varying and uncertain estimates of sepsis incidence and number of deaths. We therefore do not know how many cases of sepsis or how many deaths could have been avoided. Sepsis is a serious illness with high mortality and serious late effects. The cost of sepsis is very high, both for the affected patients and for the community. A thorough survey of the incidence of sepsis in Norway is absolutely necessary.