Some pathogens or viral vectors may easily spread via air. In that case, special attention should be paid to prevent the generation and spread of aerosols.The use of tubes with screw caps is highly recommended. And manipulations that involve a risk of aerosol formation should be performed in a class II safety cabinet.
Other organisms or viral vectors may be infectious through wounds, blood or skin contact. For those materials especially, contact contaminations should be avoided. Note that a class II safety cabinet does nothing to prevent contact contaminations! Correct working procedures are a must and skills need to be learned through training. For lentiviral vectors, especially the self-inactivating versions, the risk disappears once the vector is stably integrated into the genome and there are no infectious particles present anymore.
Primary human materials
Another category of materials that may present a risk of infection are human primary materials, that is, if their origin is unknown or the absence of infections has not been checked. The actual risk in this case also depends on the type of material. Blood presents a higher risk than for instance melanocytes, but all these materials still need to be manipulated with care under BSL2 conditions in order to avoid any risk of infection. It is worth noting that people working with primary human materials have to be vaccinated against hepatitis B.
The top 3 risky manipulations
Aerosol producing activities have already been mentioned as being risky, but even more risky is the manipulation of infectious materials in combination with sharps, especially materials that present a risk via blood contact. In addition, the most important point here is to be skilled in the art. Working carefully and knowing what you are doing. A third item that presents a high risk of infection is centrifugation. Centrifuges are known to be contamination hot spots. Therefore work with leak-free tubes and decontaminate the centrifuge regularly.