Why did many more diamond miners than gold miners die in South Africa during the 1918 influenza pandemic?

SummaryThe very large difference in mortality rates between Kimberley diamond miners and Witwatersrand gold miners during the 1918 influenza pandemic has never been explained. We examined extant epidemiological records from South African mining operations and other related activities to determine if mortality risk factors could be measured. During October 1918 when pandemic influenza struck in South Africa, the mortality rates in Kimberley diamond miners (22.4%, n = 11 445) were >35 times that of Rand gold miners (0.6%, n = 200 000). There were no differences discernable between diamond and gold miners regarding their recruitment, working conditions, housing or medical care that would explain the great variance in mortality rates. Reports of influenza-like illness in Natal Province some weeks prior to the main pandemic suggest infection from a mild version of influenza and thus protection of the gold miners from mortality whereas the more isolated diamond miners only experienced the second, more lethal, wave. The huge mortality difference between South African diamond and gold miners in 1918 is most likely explained by the circulation of a related but not identical virus to the A/H1N1 pandemic strain which reached Johannesburg prior to October 1918 because of its better transportation connections.