Table 4. Positive and negative predictive values (95% confidence limits) for 1) at least 1 CNS disease sign or symptom and 2) headache alone as predictors of meningitis for prevalences of 0.15 and 0.30.

	At least 1 sign/symptom		Headache only
Prevalence	Positive Predictive Value	Negative Predictive Value	Positive Predictive Value	Negative Predictive Value
0.15	0.19 [0.09, 0.33]	1 [0.73, 100]]	0.30 [0.14, 0.50]	1 [0.88, 1]
0.30	0.36 [0.23, 0.52]	1 [0.69, 100]	0.51 [0.33, 0.69]	1 [0.85, 1]