Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (471 page)

MYCOPLASMA PNEUMONIAE
AND
UREAPLASMA UREALYTICUM
INFECTIONS

   Definition

Mycoplasma
and
Ureaplasma
species are cell wall–deficient organisms. Cells are surrounded by a trilayer cell membrane. They are the smallest free-living human pathogens.

   Who Should Be Suspected?

   
Mycoplasma pneumoniae
is a significant cause of community-acquired pneumonia, typically presenting with upper respiratory tract symptoms and tracheobronchitis. Extrapulmonary symptoms are presumably caused by an autoimmune response to primary pulmonary infection. Extrapulmonary manifestations include arthritis, hemolytic anemia, and neurologic diseases (meningoencephalitis, cranial nerve palsy, ascending paralysis, transverse myelitis).

   
Ureaplasma urealyticum
may be detected in the microflora of genital mucosa in healthy adults, but there is evidence to link
U. urealyticum
to genital tract and neonatal infections. Infections include epididymitis, neonatal infections (pneumonia, bacteremia), nongonococcal urethritis, and orchitis.

   Laboratory Findings

Direct detection
: Because of the lack of a rigid cell wall,
M. pneumoniae
and
U. urealyticum
do not stain with Gram stain. A DNA stain, like acridine orange, may demonstrate organisms in infected tissue.

Culture
: Culture of the organism from sputum, nasopharynx, or other infected specimen shows good sensitivity but requires special culture techniques that are not widely available.

Molecular diagnostic testing
: An FDA-approved assay is available for
M. pneumoniae
.

Serology
: Serologic assays have been described for both
M. pneumoniae
and
U. urealyticum
. EIA methods are most widely used and provide good sensitivity and specificity. Accurate detection may require testing of both acute and convalescent specimens, especially in adults. EIA methods have been adapted for the detection of specific IgM.

IgM increases in the first week, peaks in the 3rd to 5th week, begins to decrease in 4–6 months but may persist ≤1 year; the interpretation of acute infection based on a positive IgM reaction, therefore, must be made with caution. The presence of IgM (>1:64) or a fourfold rise in IgG titer indicates recent infection. IgG peaks approximately 5 weeks after acute infection. IgG is unusual in the first week of infection, so repeat testing of convalescent serum is recommended. IgG titers increase for several years after acute infection.

Core laboratory
: Patients may show nonspecific signs of inflammation (mildly elevated WBCs, increased ESR) on routine laboratory testing. Cold agglutinins (agglutination of type O, Rh-negative RBCs at 4°C) may be seen in approximately 50% of patients with
M. pneumoniae
infection. Cold agglutinins, however, are not specific, and this test is not recommended for diagnosis of
M. pneumoniae
infection.

NEISSERIA GONORRHOEAE
INFECTION

   Definition

Neisseria gonorrhoeae
isolates are moderately fastidious gram-negative cocci that typically form pairs with characteristic “coffee bean” morphology. Diseases caused by
N. gonorrhoeae
are almost exclusively transmitted by sexual contact or exposure to infected genital secretions.
Neisseria gonorrhoeae
is never considered normal flora; isolates are always considered to represent infection.

   Who Should Be Suspected?

   Gonorrhea is an STD of adults. Infection in neonates may be acquired by exposure to contaminated secretions during childbirth. Infections in other prepubertal children must be investigated as a possible indication of child abuse.

   Males with gonorrhea most commonly present with urethritis, manifested by dysuria and urethral discharge. In the absence of specific antimicrobial therapy, spontaneous resolution is common. Complications include “ascending” infection (epididymitis and seminal vesiculitis, regional adenitis, abscess formation, and urethral stricture) and distant infection by contaminated secretions (e.g., conjunctivitis).

   Anorectal and pharyngeal gonorrhea may occur in men who have sex with men. Anorectal infections may be asymptomatic but often present with proctitis or rectal pain with purulent discharge and painful defecation. Pharyngeal infection may be asymptomatic but usually occurs as an acute, suppurative pharyngitis with regional adenopathy.