Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (585 page)

   
Second-line panel
: INH—high concentration, IMB—high concentration, amikacin, capreomycin, ethionamide, kanamycin, levofloxacin, ofloxacin, para-aminosalicylic acid, rifabutin, streptomycin.

Strains that are resistant to at least rifampin and INH are considered MDR (multiple drug resistant); strains resistant to at least rifampin, INH, a fluoroquinolone, and an aminoglycoside are considered XDR (extensively drug resistant).

   
Nonculture methods
: Specific mutations have been identified that confer resistance to drugs used to treat tuberculosis. For example, >95% of rifampin resistance is caused by mutation of the
rpoB
gene. Various methods may be used to detect relevant mutations, and several are commercially available (e.g., LIPA, molecular beacons).

Common core laboratory findings in active tuberculosis
:

CBC
: normocytic, normochromic anemia; WBC and differential usually normal.

Chemistry
: Hypoalbuminemia; hypogammaglobulinemia. Hyponatremia may occur due to SIADH or adrenal gland infection.

Suggested Readings

Barnes PF. Rapid diagnostic tests for tuberculosis: progress but no gold standard.
Am J Respir Crit Care Med.
1997;155:1497–1498.

Forbes BA, Banaiee N, Beavis KG, et al.
Laboratory Detection and Identification of Mycobacteria; Approved Guideline. CLSI Document M48-A
. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.

Mase SR, Ramsay A, Ng V, et al. Yield of serial sputum specimen examinations in the diagnosis of pulmonary tuberculosis: a systemic review.
Int J Tuberc Lung Dis.
2007;11:485–495.

Pfyffer GE, Palicova F. Chapter 28: mycobacterium: general characteristics, laboratory detection, and staining procedures. In: Versalovic J (ed).
Manual of Clinical Microbiology
, 10th ed. Washington, DC: ASM Press; 2011.

Steingart KR, Henry M, Ng V, et al. Fluorescence versus conventional sputum smear microscopy for tuberculosis: a systemic review.
Lancet Infect Dis.
2006;6:570–581.

Woods GL, Lin SG, Desmond EP. Chapter 73: susceptibility test methods: mycobacteria, nocardia, and other actinomycetes. In: Versalovic J.
Manual of Clinical Microbiology
, 10th ed. Washington, DC: ASM Press; 2011.

NONINFECTIOUS PULMONARY DISEASES ASSOCIATED WITH DYSPNEA

ASPIRATION PNEUMONIA

   Definition

Aspiration pneumonia refers to pulmonary disease caused by abnormal entry of fluids into the lower respiratory tract. The fluid may be endogenous secretions (e.g., gastric contents, upper respiratory secretions) or exogenous. Development of disease usually requires defective protective mechanisms (e.g., cough reflex, glottis function, ciliary transport) and aspiration of “toxic” material (e.g., particulate matter, acidic fluid, heavy bacterial contamination). Conditions that predispose to aspiration include alcoholism, seizure, CVA, head trauma, general anesthesia, dysphagia, periodontal disease, neurologic disorder, protracted vomiting, and mechanical disruption of the usual defense barriers (nasogastric tube, endotracheal intubation, upper GI endoscopy, and bronchoscopy).

   Who Should Be Suspected?

   The endogenous flora of the upper respiratory and gastrointestinal tract most commonly cause bacterial aspiration pneumonia. Polymicrobial infection, including anaerobes and less virulent streptococcal species found in gingival crevices, is typical.

   Most patients present with subacute progression of symptoms over several weeks. Common symptoms include dyspnea, cough, and purulent (often putrid) sputum production, with associated fever and weight loss. Rigors are uncommon. Symptoms of complicated infection, like abscess or empyema, may be present.

   Diagnostic and Laboratory Findings

   Microbiology: Expectorated sputum is not reliable for diagnosis, except for possibly establishing an alternative diagnosis. Culture of specimens (e.g., transtracheal or transthoracic aspirates) collected using techniques for anaerobic isolation may be informative.

   
Fusobacterium nucleatum, Bacteroides, Peptostreptococcus,
and
Prevotella
species are most commonly implicated anaerobes. Aerobic organisms, including
S. aureus
and gram-negative bacilli, are common, especially in nosocomial aspiration pneumonias.

   Core laboratory: Anemia is typical. Laboratory abnormalities associated with underlying medical conditions should be investigated that includes ABGs.