The Primary Care Differential Diagnosis of Inhalational Anthrax

Jonathan L. Temte; Andrew R. Zinkel

doi:10.1370/afm.125

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Figure 1.
Percentage of diagnoses in each of 8 diagnostic categories assigned to cases of inhalational anthrax.

CNS = central nervous system.

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Table 1.

Response Rates Based on Sex of Respondent and Location of Practice

Characteristic	Respondents No. (%)	Nonrespondents No. (%)	Final Sample %	P Value*
* Values are for tests of differences between respondents and nonrespondents.
† Men and women comprise 68.4% and 31.6% of US family physicians, respectively.¹⁷
‡ Of US family physicians, 35.0% are located in the Eastern Seaboard region; 22.6%, in the East Central region; 19.4%, in the West Central region; 6.5%, in the Mountain region; and 16.7%, in the Pacific region.¹⁷
Sex ^†				.235
Male	160 (35.7)	286 (64.3)	67.2
Female	78 (40.8)	113 (59.2)	32.8
Location of practice ^‡				.090
Eastern Seaboard region	71 (33.5)	147 (66.5)	30.6
East Central region	60 (42.3)	82 (57.7)	24.8
West Central region	51 (34.0)	99 (66.0)	21.1
Mountain region	17 (28.3)	43 (71.7)	7.0
Pacific region	40 (45.5)	48 (54.5)	16.5

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Table 2.

Primary Care Probabilistic Differential Diagnosis for Inhalation Anthrax

Diagnoses (ICD-9 Code)	Responses No. (%)	Cumulative Percentage
Note: Of the nonanthrax diagnoses, 559 were from inhalational anthrax cases, 52 from Legionella cases, and 105 from the influenza cases.
ICD-9 = International Classification of Diseases, 9th Revision; CNS = central nervous system.
1. Pneumonia (480-486)	237 (42.4)	42.4
2. Influenza (487)	56 (10.0)	52.4
3. Viral syndrome (079.99)	48 (8.6)	61.0
4. Septicemia (038)	43 (7.7)	68.7
5. Bronchitis (466)	41 (7.3)	76.0
6. CNS infection (047-049, 320-323)	35 (6.3)	82.3
7. Gastroenteritis (008-009)	21 (3.8)	86.1
8. Upper respiratory tract infection (460, 465)	17 (3.0)	89.1
9. Nonspecific febrile illness (780.9)	10 (1.8)	90.9
10. Chronic obstructive pulmonary disease (496)	8 (1.4)	92.3
11. Congestive heart failure (428.0)	7 (1.3)	93.6
12. Pulmonary embolism (415.1)	5 (0.9)	94.5
13. Tuberculosis (011.0-011.9)	4 (0.7)	95.2
14. Sinusitis (461.0-461.9)	2 (0.4)	95.6
15. Dehydration (276.0-276.5)	2 (0.4)	95.9
16. Syncopal episode (780.2)	2 (0.4)	96.3
17. Hantavirus pulmonary syndrome (480.8)	2 (0.4)	96.6
18. Adult respiratory distress syndrome (518.5)	2 (0.4)	97.0
19. Dementia (294.1)	1 (0.2)	97.2
20. Acute multiple sclerosis (340)	1 (0.2)	97.4
21. Pyelonephritis (590.1)	1 (0.2)	97.6
22. Diabetic ketoacidosis (250.1)	1 (0.2)	97.7
23. Angina (413.0-413.9)	1 (0.2)	97.9
24. Coxsackie virus infection (074.0-074.8)	1 (0.2)	98.1
25. Pleurisy (511.0-511.9)	1 (0.2)	98.3
26. Lyme disease (088.81)	1 (0.2)	98.5
27. Leukocytosis (288.8)	1 (0.2)	98.7
28. Interstitial pneumonitis (515)	1 (0.2)	98.8
29. Mononucleosis (075)	1 (0.2)	99.0
30. Pericarditis (420.0-420.99)	1 (0.2)	99.2
31. Empyema (510)	1 (0.2)	99.4
32. Aortic dissection (441.0-441.9)	1 (0.2)	99.6
33. Plague (Yersinia pestis) (020.0-020.9)	1 (0.2)	99.7
34. Tularemia (021.0-021.8)	1 (0.2)	99.9
35. Intestinal perforation (569.83)	1 (0.2)	100.0
Total	559 (100)

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Table 3.

Initial Diagnosis Provided for Cases of Fatal and Nonfatal Inhalational Anthrax, Legionella Pneumonia, and Influenza A, and Family Physicians’ Responses to Clinical Case Vignettes

			Family Physicians’ Responses
Case No.	Type	Initial Diagnosis Reported ^3, ⁷	No.	Most Common Diagnosis	Second Most Common Diagnosis
Note: The first and second most common hypothetical diagnoses are provided. For summary categories, the total numbers of responses and top 3 hypothetical diagnoses are provided. The number of cases include 9 “anthrax” diagnoses and 7 cases for which the diagnosis was not listed.
FIA = fatal inhalational anthrax; CNS = central nervous system; CHF = congestive heart failure; NFIA = nonfatal inhalational anthrax; LEG = Legionella pneumonia; INF-A = influenza A; URI = upper respiratory infection.
* Initial diagnoses of inhalational anthrax were based on workplace exposure.
† All 11 fatal and nonfatal cases.
Inhalational anthrax cases
Fatal
1	FIA	Meningitis	56	CNS infection	Sepsis
6	FIA	Viral syndrome	52	Pneumonia	Bronchitis
8	FIA	Gastroenteritis	48	Gastroenteritis	Viral syndrome
12	FIA	CHF	60	Pneumonia	CHF
14	FIA	Viral syndrome	48	Pneumonia	Influenza
Overall	FIA	. . .	264	Pneumonia, sepsis, and CNS infection
Nonfatal
3	NFIA	Pneumonia	46	Pneumonia	Septicemia
4	NFIA	Inhalational anthrax*	61	Pneumonia	Bronchitis
5	NFIA	Inhalational anthrax*	45	Pneumonia	Influenza
9	NFIA	Viral syndrome	54	Influenza	Pneumonia
10	NFIA	Inhalational anthrax*	40	Pneumonia	Influenza
11	NFIA	Bronchitis	61	Viral syndrome	Pneumonia
Overall	NFIA	. . .	307	Pneumonia, influenza, and viral syndrome
Total^†		. . .	571	Pneumonia, influenza, and viral syndrome
Other cases
2	LEG	Pneumonia	53	Pneumonia	Sepsis
7	INF-A	Influenza	50	Pneumonia	Bronchitis
13	INF-A	Influenza	58	URI	Bronchitis

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Supplemental Appendix

Appendix 1. Study instrument: letter of introduction and clinical case histories.

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Supplemental data: Appendix 1 - PDF file, 8 pages, 98 KB
The Article in Brief

Inhalational anthrax is a very rare infectious disease that resembles many other common diseases, such as influenza, pneumonia, and acute bronchitis. Because of this resemblance, patients are likely to go to their primary care doctors when anthrax symptoms arise. The resemblance to other diseases also makes inhalational anthrax difficult to diagnose. Primary care doctors have a key role to play in recognizing and responding to bioterrorism events, such as inhalational anthrax, and should be included in educational efforts for such events.