Table 1.

Estimates of Key Quantities Describing Influenza Transmission in Baltimore, Maryland, During the 1918 Pandemic, as Inferred From the Best-Fitting Model

Quantity	Value or Estimate
	No.	95% CI	%	95% CI
No. of households sampled	6,753
No. of people included in sample	28,977
No. of people reported as cases	7,140
Overall attack rate for the fall wave			24.6
Proportion of households reporting at least 1 case			47.4
Secondary attack rate within affected households			32.5
Proportion of cases which are asymptomatic and uninfectious			0	0, 6
Proportion of cases which are asymptomatic and infectious			0	0, 3
Dispersion parameter for individual variability in infectiousness (k; lower values correspond to more variability)	0.94	0.59, 1.72
Scaling parameter for infectiousness as a function of household size (α, where in-house infectiousness decreases as 1/nα)	0.35	0.22, 0.49
Effective reproduction no. (September 1–October 10), R	1.38	1.33, 1.42
Basic reproduction no., R0	1.77	1.61, 1.95
Basic household reproduction no., R0*	2.47	2.25, 2.73
Proportion of the population immune prior to September 1			22.2	17.1, 27.0
Reduction in reproduction no. on October 10			42.1	38.2, 45.7
Attack rate for a hypothetical scenario in which:
There was no prior immunity			35.8
There was no reduction in R on October 10			44.9
There was neither immunity nor reduction in R			74.2

Abbreviation: CI, confidence interval.