Retrospective Analysis of Pneumonic Tularemia in Operation Whitecoat Human Subjects: Disease Progression and Tetracycline Efficacy

Abstract

Francisella tularensis is a highly infectious Gram-negative bacterium that is the etiologic agent of tularemia in animals and humans. The incidence of tularemia is very low with a lack of comprehensive data that describe disease in humans due to difficulty in understanding time and routes of exposure. Under the title Operation Whitecoat, researchers at Ft. Detrick, MD conducted 40 clinical studies of tularemia from 1958 to 1968. In these studies, one of the objectives was to evaluate candidate countermeasures for treatment or prophylaxis of disease after exposure to Francisella tularensis strain Schu S4 by inhalation. These studies were reviewed retrospectively to delineate the early signs and symptoms or natural history of pneumonic tularemia and examine the efficacy of tetracycline in controlled human clinical studies. Using vital signs, onset of fever was objectively defined and calculated for each subject, while Adverse Events reported after exposure were also used to define the timing of disease onset and symptoms of early disease. There was a dose response relationship between time to fever onset and exposed dose at 200 cfu (172.8 h), 700 cfu (163.2 h), 2,500 cfu (105.3 h), and 25,000 cfu (75.5 h). Onset of fever was typically the earliest sign of disease at all doses but was often accompanied by symptoms such as headache, myalgia, chest pain, and nausea, irrespective of dose except at 200 cfu where only 50% of subjects exhibited fever onset or symptoms. Examining the efficacy of different treatment regimens of tetracycline, ineffective treatments were indicated by relapse of disease (fever and Adverse Events) after cessation of antibiotic treatment. Stratification of the data suggested that treatment for <14 days or doses <2g/day was associated with increased percentage of subjects with relapse of disease symptoms. Although these types of human challenge studies would not be ethically possible now, the climate post-World War II supported human testing under rigorous conditions with informed consent. Thus, going back and analyzing these unique clinical human challenge studies has helped describe the course of infection and disease induced by a biothreat pathogen and possible countermeasures for treatment under controlled conditions.

Keywords: Whitecoat; human; pneumonic; tetracycline; tularemia.

Figure 1

Representative plots of vital signs for subjects exposed to 25,000 cfu. (A–C) Representative temperature plots derived from body temperature (in °F) listings over the entire course of the study. The red vertical line represents the study day (@ 000 h) where antibiotic was administered. (D–F) Overlay plots for the same subjects in which body temperature changes (closed circles, in °F) are plotted with pulse rate (open circles) and respiration rate (X) over the first eight study days after exposure.

Figure 2

Relationship of challenge dose to time of fever onset. Time to fever onset is calculated for each subject from temperature listings (as described in the Methods) as the first time point in which the subject exhibited 2 consecutive readings ≥100°F. The data represent the calculated exposure (as described in the methods) to F. tularensis Schu S4 in those subjects exposed to a target exposure = 25,000 cfu.

Figure 3

Mean time for adverse events after inhalational exposure to F. tularensis Schu S4. For the indicated number (n) of subjects that reported the given Adverse Event, the mean study day (± SD) when each of the adverse events were first reported was calculated. The data are compared to the calculated time of fever onset [Fever (calc)] as shown in Table 2 and the mean study day when antibiotic treatment was initiated (dashed line). The data represent only subjects exposed to a target exposure of 25,000 cfu.

Figure 4

Relationship of mean time to adverse event onset to exposure dose. Mean day (± SD) of first reporting of Adverse Events upon challenge with indicated doses of F. tularensis Schu S4. (A) Represents those in the majority or all of subjects, (B) represents AEs present in about half of subjects and (C) those in about 30% of subjects. Number of subjects exposed are indicated with dose, while the number of subjects that had a particular AE are labeled above the respective bars. Fever is calculated in hours and back-calculated to days, while other AEs and antibiotic administration are only reported by day of study. Note that only 50% of subjects exposed to 200 cfu experienced fever. Any of those exposed to 200 cfu that did not get fever, also did not get treated with antibiotic and only one developed antibodies by agglutination microtiter.