The AISD virus cannot penetrate intact bodily surface, such as skin, and quickly perishes outside the human body. Consequently, AIDS id not spread by casual physical contact or by sneezing. The virus has been found in tears and saliva, but it exists there in such low concentrations that transmission from these body fluids is extremely rare. There are no known cases of AIDS transmission by insects such as mosquitoes or by domestic animals. Studies show that the virus is usually passed to an instant close to or during delivery, rather than moving across the placenta during pregnancy. Reentry infected mothers can transmit the virus to their children via breast milk. The United Stage Congress approved guideline recommending that health care workers who perform invasive procedures by tested for the AIDS virus but the testing and disclosure of results would be voluntary; no restrictions would be placed on those who tested positive.