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Can any doctors explain why do people use benzalkonium chloride or other types of Quaternary ammonium

mention that they use that to disinfect coronaviruses? Although sars cov 2 is an enveloped virus and therefore easier to break its crown like structure, publications and studies on NIMH and other journals seem to suggest that quat and benza chloride seems to be not effective against this virus. It merely reduces it's growth but do not "kill" it. Also, there are disinfecting companies claiming that they can apply a 'self-disinfecting' coat of ions on the surface and it will be potent for 6 months. I have my reservations on this. Can any doctors debunk/support such claims?
In many countries, people who have recovered are found to be infected again. And people who are infected, while recovered, have suffered long term repercussions such as pulmonary fibrosis? How likely is this in Singapore?
Also, there are claims and even a local specialist mentioned that Vitamin D might be somewhat useful in capsules. How strong is this statement?
any doctors can shed some light?
Dr. Dinesh G
Space Doctor
24 Streak Score Doctors are able to put a streak together by performing an activity everyday
Hi @BusinessJing thank you for your questions! There's alot to unpack here and I will try to answer them one by one. With respect to the role of benzalkonium chloride/quat, I am not able to identify any robust studies that support these conclusions. Also, the claims of "self-disinfecting" coat that I could find from companies online also are not substantiated by any robust evidence as you rightly pointed out. 

With regards to re-infections, studies are being conducted locally and abroad to understand this risk. One consideration is that existing reports of re-infections from other countries are based on the use of early versions of COVID-19 tests that became available at the start of the outbreak. These are imperfect with high rates of false positives/negatives reported in various cross-validation studies. 

Therefore, it is possible that the patient(s) in question may have had a false negative test, whereby subsequent testing was a true positive and may have wrongly led to the conclusion of re-infection. In other words, with studies still ongoing, it is still too early to make any conclusions about this. Fortunately in Singapore, we have taken a conservative approach to guard against this by only considering patients as "recovered" after multiple consecutive negative tests.

Long-term repercussions such as pulmonary fibrosis are driven by the disease rather than the context (aside from variations in national mortality rates), and will likely be the same in Singapore as they are elsewhere. The claim about vitamin D does not appear to be based on any definitive evidence that I can find.
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