Sure, round figures, lets call it 800K. And I bet the vast majority of them knows. It doesn’t take much of an examination for a doctor to determine location of heart and liver.
In fact many of them don’t, since the body is mostly symmetrical and apart from cutting them open or doing an MRI, you can’t really tell (which isn’t a big deal in most cases, because most medical procedures work regardless of this condition). Also, the heart is located almost in the middle, so there is not much difference.
Listening to the chest with a stethoscope, or your ear will tell the location of the heart. Percussing over the liver, but not finding a solid structure e.g. liver, which sounds different than a hollow structure, e.g. lungs would also help in identifying unexpected organ locations. I’m curious how you came to know that many of them don’t know? Do you keep a register of people with this condition, but don’t tell them?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8901252/
It is difficult to provide a valid estimation of real frequency. There are only a few own observations in the literature and a lot of citations.
We performed a search in our radiologic database, looking for situs inversus as key words in the results. Between 2006 and 2020, 217,646 imaging examinations (ultrasound, CT and plain radiography) were performed at the Department of Transplantation and Surgery, Semmelweis University. Out of them, 21 cases were found, which represents a 1:10,000 frequency. This hospital-based prevalence rate best reflects Adams et al in 1937 (23:232,113), and Lin et al in 2000 (20:201,084) from Massachusetts, as data from own observations.26 This rate is similar as well to the population-based Baltimore-Washington Infant Study.12 SIT is slightly more frequent in males: 1.5:1.27
https://www.healthline.com/health/situs-inversus#symptoms
Because the condition seldom causes symptoms and is so rare, a person may not know they have it. And it may not be discovered until visiting a doctor for a different reason.
https://my.clevelandclinic.org/health/diseases/23486-situs-inversus
You may not develop any symptoms with situs inversus. Although your organs are reversed, they’re often still functional. So you wouldn’t notice any signs or complications.
Of course, trying to estimate how many people don’t know about a disease is a difficult task, but the general consensus is the condition is rare and often doesn’t produce any symptoms, as such there are definitely many people with the condition that haven’t even ever heard of it.