Table 2. Effect of spatial patterns of ANC attendance on ANC surveillance estimates for HIV prevalence in small towns in Manicaland, Zimbabwe.

	2001-2003				2003-2005				2006-2008				2009-2011
	ANC attendees			Pregnant women	ANC attendees			Pregnant women	ANC attendees			Pregnant women	ANC attendees			Pregnant women
Place of residence	% HIV+	n	n/N	% HIV+	% HIV+	n	n/N	% HIV+	% HIV+	n	n/N	% HIV+	% HIV+	n	n/N	% HIV+
Towns	33.9	59	0.29	34.6	27.5	40	0.20	30.2	17.9	39	0.18	25.3	7.7	39	0.19	19.1
Estates	13.6	22	0.11	22.4	26.1	23	0.12	14.6	0.0	5	0.02	12.1	28.6	7	0.03	11.6
Villages	16.7	120	0.60	20.4	10.4	134	0.68	12.8	12.9	170	0.79	15.0	11.2	161	0.78	10.7
Alla	21.4	201	1.00	24.7	15.7	197	1.00	16.5	13.6	214	1.00	16.8	11.1	207	1.00	12.3
Participation biasb	74.5%				94.6%				72.5%				85.3%

^aThe figures in italics indicate HIV prevalence rates in pregnant women standardised by place of residence, based on the residence distribution of ANC attendees.

^bContribution of ANC attendees resident in surrounding rural areas to under-statement of HIV prevalence in urban pregnant women.