The Risk of Post-Polio Syndrome Among Immigrant Groups in Sweden
POST-POLIO ARTICLE REVIEW:
I was excited when I saw a paper published in 2023 about the incidence of polio and PPS. The authors used the Swedish National Patient Register (NPR) as the data source, a database that is incredibly complete, capturing 99% of inpatient and 97% of outpatient diagnoses and associated information, and providing just over 1 million polio survivor subjects for the study.
The authors performed multiple complex, graduate-level statistical analyses. But I found that the more statistical analyses performed, the less I was learning about polio and PPS. I've converted the fancy statistics to percentages and I'm interested in your take.
The Risk of Post-Polio Syndrome Among Immigrant Groups in Sweden
INTRODUCTION
The percentages of immigrant polio survivors and those diagnosed with post-polio syndrome were compared to Swedish-born polio survivors using the Swedish National Patient Register (NPR) The NPR records data on medical diagnoses in inpatient and outpatient specialist care. The NPR also records demographic information e.g., age, gender, marital status, years of education, socioeconomic status and place of residence.
These data from 1998 through the end of 2018 were collected for native–born Swedes and immigrants to Sweden 18 and older who were polio survivors.
The goal of this study was to examine the incidence of polio and PPS in foreign-born immigrants as compared to native-born Swedes.
RESULTS
Compared to a total Swedish population of 6.18 million, there were 5,300 polio survivors (.086% of the population) with 4,307 Swedish–born (81%) and 993 foreign-born (19%). The incidence of polio among immigrants as compared to the Swedish-born was higher in men by 77% and by 38% in women. The incidence of PPS in immigrants as compared to the Swedish-born was higher in men by 77% and by 46% in women.
Not surprisingly, 90% of native–born Swedish polio survivors were aged 50 or older, while 50% of immigrants were younger than 40. Also not surprising, and as we found in our 1985 U.S. National Post Polio Survey, a larger percentage of polio survivors were married (68%) versus the general population (57%) and had more than a high school education (25%) versus the Swedish population (23%).
Other diagnoses. Swedish-born male polio survivors were at higher risk of hypertension, stroke, depression and cancer, while immigrant men only had a higher risk of stroke. Swedish-born female polio survivors were at higher risk for hypertension and cancer, while immigrant female polio survivors were at no higher risk for any condition.
The Geography of Polio and PPS.
Statistical analyses removed the effects of age, education, other medical diagnoses, marital and socioeconomic status from the data to calculate the incidence of polio and PPS in immigrants as compared to native–born Swedes.
Consulting the Table on page 1, and combining males and females, polio was 156% and PPS 207% higher in immigrants as compared to the Swedish-born population. Combining Asian and African immigrants, it was no surprise that polio was 560% higher and PPS 506% higher as compared to the Swedes.
Among Europeans, the incidence of polio was 43% lower and PPS 12% higher. Among Russian immigrants the incidence of polio was 57% lower than among Swedes. However the incidence of PPS in Russian males was 193% higher.
DISCUSSION
The data collection and statistical analyses in this study were a Herculean undertaking. Unfortunately, the paper tells us about the incidence of polio and PPS in Swedish immigrants but little we don’t already know about the incidence of polio and PPS throughout the world.
Also unfortunate, the paper seems more about applying complex data analysis than using the data to help identify factors that may cause, exacerbate or potentially reduce PPS symptoms. Instead of using statistics to remove the effects of diabetes, hypertension, heart disease, stroke, depression and osteoporotic fractures, these conditions could have been analyzed to describe their effects in polio survivors and potentially their relationship to PPS.
Even more unfortunate - and confusing - is the way in which the authors organized the paper and their inconsistency with naming, referring to subjects who had had polio as “post–polio" in most instances, but as "polio", "sequelae of poliomyelitis”, "polio patients" and "polio survivors" in others. Subjects having PPS are most often identified as such, but also are referred to as having “post-polio myelitic syndrome” and “post-polio syndrome.”
The inconsistency with naming reminds us of the flaws in using large population databases: you can't know with consistency the criteria doctors are using to make their diagnoses - here of polio and especially PPS - that they then input to the database. How many polio survivors in any country have had the experience of going undiagnosed or being given an incorrect diagnosis?
Fortunately, the authors come to a conclusion we all can support:
“It is of importance to be aware of PPS in the whole health care system in Western countries . . .
PPS patients need treatment and follow-up for their lifetimes. PPS will only disappear decades after the worldwide eradication of polio."