Table 1. Epidemic Intelligence Service field investigations involving unknown agents and potential agents of bioterrorism, 1988–1999.
| Agent | Frequency | % of investigations (n = 1,099) |
|---|---|---|
| Unknown infectious agenta |
41 |
3.7 |
|
Vibrio choleresis
|
18 |
1.6 |
|
Yersinia pestis
|
11 |
1.0 |
| Viral hemorrhagic fever virus |
7 |
0.6 |
|
Bacillus anthracis
|
3 |
0.3 |
|
Clostridium botulinum
|
3 |
0.3 |
|
Coxiella burnetii
|
1 |
0.1 |
|
Francisella tularensis
|
1 |
0.1 |
| Total | 85 | 7.7 |
aIn these cases, the outbreak was considered to be caused by an infectious agent because of the characteristics of the illness and outbreak.