The USOC is providing its 600-plus athletes with special air masks, which they have the option of wearing out on the streets. The masks are not intended to be worn during training or competition but some athletes have said they are considering wearing them.
New Zealand's athletes have been issued face masks as part of their standard team equipment while team managers have advised athletes to wear masks around the Olympic village but not during competition.
Japan distributed masks normally used on construction sites to its national team.
