Option 1: Smoking and drinking alcohol. This option is incorrect. Smoking and drinking alcohol are not direct risk factors for the transmission of HIV infection. While these behaviors may have negative effects on overall health and immune system function, they do not directly contribute to the transmission of the virus.

Option 2: Observing bad hygiene. This option is not mentioned in the provided correct answer. However, observing bad hygiene practices such as not washing hands regularly or not properly cleaning instruments used in medical procedures can potentially increase the risk of transmission if the HIV virus is present.

Option 3: Blood transfusion. This option is mentioned in the correct answer. Blood transfusions can be a risk factor for HIV transmission if the blood used is not properly screened for the virus. However, current blood transfusion practices adhere to strict screening protocols to minimize the risk of infection.

Option 4: Unprotected sex. This option is mentioned in the correct answer. Unprotected sexual intercourse, particularly vaginal or anal sex without the use of a condom, is a primary mode of HIV transmission.

Overall, the correct answer is option 2, which includes blood transfusion and unprotected sex as risk factors for the transmission of HIV infection.