are inactivated by soap and water. furthermore, the virus can also be easily destroyed using common hygiene techniques and detergents, disinfectants and antiseptics. environmental factors which are important for hpiv survival are ph, humidity, temperature and the medium within which the virus is found. the optimal ph is around the physiologic ph values (7.4 to 8.0), whilst at high temperatures (above 37 °c) and low humidity, infectivity reduces. the majority of transmission has been linked to close contact, especially in nosocomial infections. chronic care facilities and doctors' surgeries are also known to be transmission 'hotspots' with transmission occurring via aerosols, large droplets and also fomites (contaminated surfaces). the exact infectious dose remains unknown. economic burden in economically disadvantaged regions of the world, hpiv infection can be measured in terms of mortality. in the developed world where mortality remains rare, the economic costs of the infection can be estimated. estimates from the us are suggestive of a cost (based on extrapolation) in the region of $200 million per annum.