PhD thesis - University of Hertfordshire Research Archive

and improve response during the study period, this latter effect was beyond
control.
Table 3. Response rates by health authority over the surveillance period.
Health Authority
Question-
naires
Isolates Response
(%)
42
Response by
study year
1 2 3
Barnet Enfield and
Haringey
510 206 248 95 270 470
Birmingham 2007 2829 71 74 71 67
Bradford 1079 200 540 214 ∞ ∞
Bro Taf 537 1245 43 0 108 50
North Cumbria 0 682 0 0 0 0
Dyfed Powys 104 587 18 31 16 0
East Kent 684 1082 63 9800 40 32
Hereford 386 150 257 86 ∞ ∞
Lancashire † 1264 2669 47 40 56 50
Leeds 2084 3307 63 67 64 57
Leicester 1255 1464 86 109 87 62
Manchester ‡
4780 4613 104 89 122 112
North Devon 1027 1823 56 59 66 42
North Essex 1181 1506 78 69 92 75
Nottingham 1872 2541 74 73 85 62
Southampton and south 1617
west Hampshire
1793 90 102 108 54
Total 20387 26697 76 74 86 69
* , Questionnaires received as a percentage of isolates referred; † ,North West and South Lancashire health
authorities; ‡ , Bury and Rochdale, Manchester, Salford and Trafford, Stockport, West Pennine & Wigan and Bolton
health authorities.
Figure 4 overleaf shows the age distribution of cases where isolates were
received and questionnaires referred. Whilst the two datasets appear to be
generally comparable, some subtle differences are apparent. Young adults
were under represented amongst the questionnaire data and the opposite is
true for older adults and the elderly. The latter reflects the fact that this age
group is notoriously difficult to recruit into epidemiological studies. At the
other end of the spectrum, older people may be retired and therefore have
more free time to complete and return questionnaires.