Two people died of malaria and two others succumbed to leptospirosis on Sunday.
Malaria claimed the life of a 32-year-old man from Malad and a 40-year-old man from Byculla.
Thirteen people have died of the disease so far in August and public hospitals have admitted more than 1,700 malaria patients. On Monday alone, public hospitals reported admitting 124 new malaria patients.
An 18-year-old boy from Colaba and a 27-year-old man from Mazgaon died of leptospirosis, which has claimed three lives in August. Three people suffering from leptospirosis were also admitted to public hospitals on Monday.
Nine more people also tested positive for swine flu on Monday, taking the total number of H1N1 cases in the city to 91 this month.
Among other rain-related illnesses, public hospitals reported 504 cases of fever, 45 cases of gastroenteritis and three cases of dengue.