Table 1.

Derivation of multipliers to estimate incidences of Q fever and spotted fever group rickettsioses (SFGR) in the Moshi Rural and Moshi Urban Districts, Kilimanjaro Region, Tanzania

	Multiplier equation	Study period
		2007–2008				2012–2014
Q fever IFA sensitivity multiplier	1/sensitivity	1/1		1		1/1	1
Q fever IFA specificity multiplier	Specificity	0.95		0.95		0.95	0.95
SFGR IFA sensitivity multiplier	1/sensitivity	1/0.94		1.06		1/0.94	1.06
SFGR IFA specificity multiplier	Specificity	1		1		1	1
KCMC multiplier	No. of households interviewed/no. households seeking care at KCMC for fever ≥ 3 days
Age 0–4 years		198/17		11.65		198/17	11.63
Age 5–14 years		361/10		361/10		361/10	36.10
Age ≥ 15 years		810/35		23.14		810/35	23.14
MRRH multiplier	No. of households interviewed/no. households seeking care at MRRH for fever ≥ 3 days
Age 0–4 years		198/67		2.96		198/67	2.96
Age 5–14 years		361/137		2.64		361/137	2.64
Age ≥ 15 years		810/299		2.71		810/299	2.71
Paired sera multiplier	No. of patients included in the study/no. of patients included in the study with paired sera	Q fever	SFGR	Q fever	SFGR
Age 0–4 years		256/143	256/124	1.79	2.06	430/177	2.43
Age 5–14 years		59/45	59/42	1.31	1.40	111/87	1.28
Age ≥ 15 years		274/156	274/141	1.76	1.94	573/377	1.52
Time multiplier	No. of days in a week/no. of enrollment days per week	7/5		1.40		7/5	1.40
Enrollment multiplier	No. of eligible patients/no. of patients enrolled in fever surveillance	1,310/870		1.51		2,962/1,414	2.09
Study duration adjustment	No. days per year/study duration (in days)	365/349		1.05		365/828	0.44

IFA = indirect immunofluorescence assay; KCMC = Kilimanjaro Christian Medical Centre; MRRH = Mawenzi Regional Referral Hospital; SFGR = spotted fever group rickettsioses.