Pseudomonas aeruginosa infection: This is likely due to the exposure to seawater, which can be contaminated with Pseudomonas species. The characteristic "dead fish" smell is consistent with infections caused by this bacterium, which is known to produce a blue-green pigment called pyocyanin and has a distinct odor.

Vibrio species infection: Given the exposure to seawater from the Arabian Gulf, Vibrio species, which are naturally found in marine environments, could be a cause of the infection. Some Vibrio species can cause infections with foul-smelling discharge.
Staphylococcus aureus infection: This bacterium is a common cause of skin and soft tissue infections and could potentially infect the nasal passages and sinuses, especially if there was trauma or irritation from the seawater.
Mixed bacterial infection: The presence of purulent discharge suggests a bacterial infection, and given the exposure to seawater, a mixed infection involving multiple species of bacteria is possible.

Malignant otitis externa: Although less common, this condition, caused by Pseudomonas aeruginosa, can occur in individuals with compromised immune systems. It is characterized by severe infection of the outer ear and skull base and can be life-threatening if not promptly treated.
Cerebral abscess or meningitis: In rare cases, bacterial infections of the sinuses can spread to the brain, causing abscesses or meningitis. These conditions are medical emergencies and require immediate attention.

Marine fungal infections: Fungi found in marine environments could potentially infect the nasal passages and sinuses, although this would be less common than bacterial infections.
Parasitic infections: Certain parasites found in seawater, such as those causing myiasis (infestation by fly larvae), could potentially infect the nasal passages, although this would be extremely rare and usually associated with specific travel or exposure histories.