Subdividing viral targets into families, we used an updated set of sequences, downloaded 5 February 2009. For familylevel primers, we computed primer sets using three alternative parameter settings (Table 1) : (i) 17-21-mer primers with T m = 55-60 C, primers not checked for uniqueness; (ii) same length and T m specifications as in (i) but eliminating from consideration as primers any oligos of at least 17 nt that occur in nontarget viral families, as described earlier; and (iii) 10-15-mer primers with T m = 40-45 C. These primers are available as Supplementary Data.