Table 2. Risk for bias in studies on human-to-human transmission of plague*.

Study	Were patient characteristics adequately reported?	Was there some effort to trace all contacts from the index case?	Were the methods used for tracing contacts adequate?	Were the laboratory methods used for defining a confirmed case of plague reliable?	Was the route of transmission plausible?	Was the cause-effect of transmission plausible?
Almeida et al. (17)	Partial	Unknown	NA	Yes	No	Unknown
Begier et al. (25)	Yes	Yes	Yes	Partial	Yes	Yes
Bertherat et al. (26)	No	Partial	Unknown	Yes	Yes	Yes
Evans et al. (18)	Yes	Unknown	NA	Yes	Yes	Yes
Kellogg et al. (20)	Yes	Unknown	NA	Yes	Yes	Yes
Kugeler 2015 (19)	Partial	Unknown	NA	Yes	Unknown	Unknown
Rabaan et al. (21)	Partial	Partial	Unknown	Yes	Yes	Yes
Ramasindrazana et al. (22)	Yes	Yes	Yes	Yes	Yes	Yes
Ratsitorahina et al. (23)	Yes	Yes	Unknown	Partial	Yes	Yes
Richard et al. (24)	Yes	Yes	Unknown	Yes	Yes	Yes

*NA, not applicable.