True statement regarding poliomyelitis is:

Option 1, 2 Poliovirus is susceptible to pasteurization, heat. Resistant to low pH and bile and proteolytic enzymes of intestine. For every clinical case, there may be 1000 subclinical cases in children and 75 in adults. (In the question above, cases in adults are 1000. Hence, it is not true.) Option 3 Transmission: MC is feco-oral route, or rarely by inhalation or conjunctival contact. Option 4 Most outbreaks of polio are due to type-I poliovirus whereas vaccine induced poliomyelitis is due to type 3.