All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If your intention, by buying shares in the hospital, was to benefit from the revenue of the hospital rather than to trade in the shares themselves, then you should pay Zakah on those shares as exploited things, like rented real estate and land. That is, no Zakah is due on you for the value of the shares, but only for their profit if it reached the due Nisaab by itself, or by other money or articles of merchandise that is joined to it, and a lunar year elapsed on it from the moment of holding it, in which case, you should give out one-fortieth (2.5%). If they have no revenue, or it has not reached the due Nisaab, or a full lunar year has not elapsed on it, then no Zakah is due.
But if your intention was to trade and make profits from the shares, then you should pay Zakah on them as articles of merchandise; at the end of each lunar year you should calculate the value of the shares and give one-fortieth (2.5%) of the value, whether or not they have incurred any profit, and whether their value increased or decreased, compared to the price for which you purchased them. Since their Zakah has not been paid for the last three years, it should be given immediately, because you are still liable for it. That is so if you bought the shares with the intention of trading in them as we explained above.
Allaah Knows best.