Yesterday, I posted a piece examining the oft-quoted mortality rate for measles of one to two deaths per thousand cases of infection. Today, I want to look at what can be learned from more recent and more comprehensive dataset – this one from the 2008-2011 measles outbreak in France.
In the early 2000’s, measles was a relatively rare occurrence in France. From 2008 to 2011 though, there was a dramatic increase in cases – peaking at over 3,000 new cases per month being recorded in 2011. Because the outbreak occurred in a developed country where the disease was no longer considered a pressing pubic health issue, it provides a unique opportunity to estimate mortality rates following infection by the virus in economies with robust healthcare systems.
In 2013, Denise Antona and co-authors published a comprehensive assessment of the outbreak in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases. Over the four year study period, there were 22,178 documented cases of measles. 11.6% of cases (2,582) involved complications , including pneumonia (1,375 cases, 6.2%), acute otitis media (321 cases, 1.4%), and hepatitis or pancreatitis (248 cases, 1.1%). According to the paper’s authors, diarrhea was reported in 100 cases (0.4%). Overall, there were ten deaths reported (0.05%).
The data are particularly useful for examining morbidity and mortality rates associated with measles in a developed country like France, as with the relative novelty of the disease, the number of reported cases is likely to have been substantially higher than in earlier decades when the disease was commonplace.
In table 1 below (based on Antona et al.’s paper), the number of measles-related complications per 10,000 cases of infection is given for different health impacts and age ranges, based on individuals who were hospitalized.
Focusing specifically on mortality, the overall rate was 4.5 deaths per 10,000 documented cases of measles. The rate was highest amongst individuals 30 years old or more (7.2 deaths per 10,000 documented cases), with those between 15-29 years old having a mortality rate of 6.9 per 10,000 documented infections. There were no deaths recorded amongst the 1,663 children under the age of one who were documented as contracting measles.
The paper’s authors also split the documented deaths between patients who were immunodeficient, and those who were not. Of the ten patients who died, one had congenital immunodeficiency and six had acquired immunodeficiency (e.g., Hodgkin’s lymphoma, Crohn’s disease, HIV, immunosuppressive treatment). In other words, only 3 out of the 10 deaths recorded were associated with non-immunocompromised individuals.
The overall mortality rate of around 4-5 deaths per 10,000 cases of measles for all individuals is slightly higher than the estimate based on historic US data. However, it doesn’t account for underreporting of measles infections, which the paper’s authors estimate at something over 50%.
Adjusting the data in table 1 by assuming only 50% of measles cases were reported gives the morbidity and mortality rates estimated in table 2 (below).
The overall mortality rate here is reduced to 2.3 deaths per 10,000 cases of measles. This value still reflects considerable uncertainty – there are likely to have been more non-fatal complications than were recorded with hospitalized patients for instance, meaning that estimated morbidity rates are probably substantially underestimated. However, it is less likely that there were substantially more measles-related deaths than were reported by Antona et al. It is also consistent with analysis of US data which suggest a mortality rate of the order of 1 in 10,000 for infected individuals.
That said, the morbidity and mortality rates presented here only tell part of the story. As was seen with the immunocompromised patients in the study, susceptible sub-populations may face a significantly greater risk from measles. This becomes a particular issue where there is an increasing probability of them coming into contact with infected individuals – as is the case where immunization isn’t widespread.
Nevertheless, the evidence from the French outbreak is strongly suggestive that, for infected individuals living in a developed economy with a robust healthcare system, the mortality rate is most likely less than 2-3 deaths per 10,000 cases.