Learn Italian: Siamo sfortunati, questo albergo è scomodo e sporco. - We are unlucky, this hotel is uncomfortable and dirty.

It acts as a negative prefix that completely reverses the meaning of the base adjective, much like 'un-' in English. Since fortunato means 'lucky' and comodo means 'comfortable', adding s- turns them into 'unlucky' and 'uncomfortable'.

Since we are learning about the negative s- prefix, is sporco (dirty) another example of this?

No, it just happens to start with the letter 's'! sporco is a base root word on its own. While the s- prefix is very common before consonants, you will still encounter plenty of regular words that just naturally start with an 's'.

Why is sfortunati plural, while scomodo and sporco are singular?

Adjectives in Italian must match the gender and number of the noun or pronoun they describe. sfortunati describes the plural 'we' (from the verb siamo), so it ends in -i. scomodo and sporco describe questo albergo (this hotel), which is masculine singular, so they take the singular -o ending.

Could I use the word hotel instead of albergo here?

Yes, Italians use the loanword hotel all the time, and it means the exact same thing as albergo. If you used it here, the sentence would simply be questo hotel è scomodo e sporco.