Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (464 page)

Campylobacter
species are microaerophilic, curved GNBs.
Campylobacter
species cause diarrheal infections globally and are the most common bacterial cause of significant diarrheal illness in most countries.
Campylobacter jejuni
is the most important human pathogen. In developed countries, asymptomatic infection is uncommon.

   Who Should Be Suspected?

Infection is usually acquired by contact with animals, mainly poultry, in which
Campylobacter
species are common components of endogenous gut flora. Personto-person transmission is uncommon. Most infections resolve within 7 days.
Campylobacter
GI infection typically results in diarrhea with fever, cramping, and vomiting. Blood may be present in the stools. A nonspecific colitis, with marked fecal leukocytes, is common. Guillain-Barré syndrome has been associated with campylobacteriosis. Disease outside the GI tract is uncommon. Septic arthritis, bacteremia, proctocolitis, meningitis, and other infections have been reported.

   Laboratory Findings

Culture
: The special culture procedures required for isolation of
Campylobacter
species are included in routine stool culture protocols in clinical microbiology laboratories.

CHLAMYDIA AND CHLAMYDOPHILA INFECTIONS

   Definition

Chlamydia
and
Chlamydophila
species are obligate intracellular bacterial pathogens.

   Who Should Be Suspected?

The Chlamydiaceae are responsible for a number of distinctive disease syndromes, including

   
Chlamydia genital tract infection
.
Chlamydia trachomatis
is the most common cause of sexually transmitted bacterial infections in industrialized nations; serovars D through K are responsible for these genital infections. Serovars L1, L2 (including a and b variants), and L3 are responsible for lymphogranuloma venereum (LGV), a systemic STD most commonly encountered in developing countries.

Most sexually transmitted
C. trachomatis
infections are asymptomatic, contributing to their spread. Common clinical manifestations include urethritis, mucopurulent cervicitis, ascending infections, female genital tract conditions (PID, endometritis, salpingitis, perihepatitis syndrome), male genital tract problems (epididymitis), conjunctivitis (nonscarring), and proctitis. Complications of
C. trachomatis
genital infection may include scarring of the fallopian tubes, infertility, and ectopic pregnancy. Maternal
C. trachomatis
infection at the time of delivery may result in neonatal infection, which typically manifests as conjunctivitis or pneumonia. Acute, nonscarring inclusion conjunctivitis occurs in 18–50% of infants of mothers with untreated genital infection.

   
Trachoma
: Trachoma refers to chronic
C. trachomatis
conjunctivitis, usually caused by serovars A, B1, B2, and C. Infection leads to corneal scarring and, in late stages, blindness.

   
Chlamydophila pulmonary infections
(
Chlamydophila pneumoniae
and
Chlamydophila psittaci
):
C. pneumoniae
is most commonly associated with lower and upper respiratory tract infections (e.g., pneumonia, bronchitis, sinusitis). This pathogen has been implicated in a significant minority (approximately 15%) of community-acquired cases of pneumonia.

Chlamydophila psittaci
infection causes psittacosis. Birds are the natural reservoir for this organism; infectious forms may remain viable in the environment for extended periods. Human infection is easily transmitted by inhalation of infectious organisms directly shed from birds or from organisms in their environment. Patients usually present with nonspecific symptoms in acute infection, including flu-like illness: fever, severe headache, hepatomegaly, splenomegaly, and GI symptoms. Chronic pneumonitis may develop.

   Laboratory Findings

Molecular diagnostic testing
: NAATs are considered the gold standard for the diagnosis of genital
C. trachomatis
infections. FDA-approved kits are available for endocervical, urine, urethral specimens, and liquid-based Pap test specimens. The sensitivities reported for NAATs range from approximately 90 to 97%; the specificities are >99%. NAATs have been described for detection of
C. pneumoniae
and
C. psittaci
, but FDA-approved kits are not available, and their performance has not been clearly defined.

Culture
: Isolation of
C. trachomatis
in culture remains an important technique for diagnosis of nongenital infections and is considered the standard for evidence in medicolegal cases, such as rape and child abuse. For optimal isolation, it is critical to collect samples that contain the host cells infected by chlamydia and to transport in conditions that will maintain the viability of the organisms. For detection of genital infections, the sensitivity of tissue culture is approximately 65–85%, with specificity near 100%.

Direct detection
: DFA staining kits are available for direct detection of
C. trachomatis
from genital specimens. Slides require examination by an experienced laboratorian, and slides must be carefully evaluated to ensure adequate specimen collection (i.e., the presence of columnar epithelial cells). Under optimal conditions, the sensitivity of DFA is approximately 60–80% with specificity >98%. Typical intracytoplasmic inclusions in epithelial cells of Giemsa-stained smears from conjunctival scrapings are found in 50% of patients with
C. trachomatis
conjunctivitis.

EIA detection
: A number of EIA kits for the diagnosis of
C. trachomatis
genital infection are commercially available. Sensitivities of approximately 60% are reported for cervical infections. Reported specificity is high, but false-positive reactions are possible for tests based on detection of
C. trachomatis
lipopolysaccharide.