That is not correct, the legislation is very clear that such data is only covered where it is contains sufficient detail to identify the individual concerned. Once detail has been redacted from a file so that the individual is no longer identifiable, GPRD does not apply.
It would be ridiculous to think that GDPR would prevent a company seeking advice from a specialist as to how they should handle a scenario where an unidentified employee contracts a contagious disease. The data protection commissioner ever went further in the 2013 report as referenced above.
It doesn't prevent it Leo but it's not as simple as that. There is a whole section on how sensitive personal data is collected, stored and shared. You are only talking about redaction when sharing data which is fine from a security point of view but it doesn't absolve the company from other parts of GDPR legislation. Just because the data is redacted doesn't mean GDPR doesn't apply. The legislation still applies. Article 6 and Article 9 still apply. A company can't just share redacted sensitive personal data anytime it wants. A company of two people in a small town. Secretary takes a medical exam. Manager has no idea what it means so sends it on to local doctor without any identifiable employee details and without asking for the employees consent. Doesn't take rocket science for the doctor to figure it out. I know it's not realistic but the legislation is in place to prevent things like this happening.
The idea that companies can just process sensitive personal data as they see fit is dangerous even it is not identifiable.