The National Aids Control Council yesterday said HIV is spreading faster in towns served by the 476-km railway line.
The spike in select counties dealt a major blow to the momentum of new infections which have fallen nationally.
NACC said compared to 2013, new infections rose by more than 50 per cent in all Coast counties.
They also rose by more than 50 per cent in the Lapsset corridor since 2013.
This corridor includes Lamu county where a seaport is being built, and Marsabit and Wajir, which are served by the brand new road that connects Kenya to Ethiopia.
The pattern mirrors the spread of HIV in the 1980s and 1990s along transport corridors, largely blamed on long-distance truck drivers.
Source: The Star