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# Long description

In this graph, the horizontal axis is marked in years from 1994 to 1997. The vertical axis is labelled number of isolates per week and is marked from zero to 900 at intervals of 100. The data show that there were three separate epidemics, which occurred over the three successive winters, and in increasing order of severity. The peak numbers of isolates were as follows: in 1994/5, there were 370; in 1995/6, there were 630; and in 1996/9, there were nearly 900.