This outbreak of bubonic plague in England is thought to have spread from the Netherlands, where the disease had been occurring intermittently since 1599. It is unclear exactly where the disease first struck but the initial contagion may have arrived with Dutch trading ships carrying bales of cotton from Amsterdam, which was ravaged by the disease in 1663–64, with a mortality given of 50,000. The first areas to be struck are believed to be the dock areas just outside London, and the parish of St Giles. In both of these localities, poor workers were crowded into ill-kept structures. Two suspicious deaths were recorded in St Giles parish in 1664 and another in February 1665. These did not appear as plague deaths on the Bills of Mortality, so no control measures were taken by the authorities, but the total number of people dying in London during the first four months of 1665 showed a marked increase. By the end of April, only four plague deaths had been recorded, two in the parish of St. Giles, but total deaths per week had risen from around 290 to 398.Leasor (1962) pp. 46–50
