South Africa's many ports and harbours rendered it vulnerable to infections passed on by sailors. The war and the migrant labour system also meant that large groups of men regularly travelled long distances, spreading infections throughout the country by doing so.
South Africa boasted a well-developed railway system in 1918 covering 10 000 miles, and this enabled the flu to spread rapidly to remote rural areas. Many railway workers indeed succumbed to the flu, and many of those who did not were seconded to do relief work, assisting medical staff, distributing medical supplies and running soup kitchens.
Furthermore, South Africa also has a large indigenous population living under poor conditions. These people also had very little access to medical facilities or knowledge.
Map: the spread of the 1918 flu in SA
Map: the spread of the 1918 flu
Sources for the whole section on the 1918 epidemic in South Africa: SA Railways and Harbour Magazine, December 1918; Phillips, Howard. South Africa's worst Demographic Disaster: The Spanish Influenza Epidemic of 1918. (South African Historical Journal, (20), 1988.