Vol. 20, No. 21
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, May 22, 2001
4 outbreaks were reported to DHMH during MMWR week 20 (May 13-19, 2001):
2 outbreaks of foodborne gastroenteritis;
1 associated with a food-service facility (Frederick Co.),
1 associated with a cruise ship and is confirmed as Salmonella (cases
are Anne Arundel Co. residents),
1 outbreak of gastroenteritis at a nursing home (Wicomico Co.)
1 outbreak of conjunctivitis at an adult daycare center (Queen Anne's
Co.)
Organism: Trichomonas vaginalis is one member of a family of flagellated protozoa called trichomonads. Trichomonads are widespread in nature and cause disease in cattle and fowl, in addition to human beings. Members of the family that infect human beings also include Trichomonas tenax and Pentatrichomonas hominis. The site of infection of trichomonads are highly specific. For instance, T. tenax can occasionally infect the respiratory tract in patients with pre-existing pulmonary disease. P. hominis is sometimes found infecting the lower gastrointestinal tract in patients with symptomatic bowel disease. T. vaginalis, on the other hand, only infects the genitourinary tract1.
T. vaginalis is a motile, pear-shaped protozoan measuring 10 x 7 microns in dimension. It has four free anterior flagella arising from a single stalk and a fifth flagellum located in a undulating membrane that extends about halfway across the organism [Figure 2]. A variety of carbohydrates can be used for energy production. The protozoa are capable of ingesting bacteria, leukocytes, erythrocytes, and epithelial cells. T. vaginalis reproduces by binary fission. No cyst forms exist. Strains are determined by serotype, size, surface carbohydrate and protein expression, hemolytic activity, and experimental virulence. Specific virulence factors, however, have not been conclusively characterized1.
T. vaginalis infection (trichomoniasis) is a sexually transmitted disease. It occurs in 3 million women in the U.S. annually. The general infection rate for men, however, is unknown. It has been reported in 17% of HIV-infected women and 9-22% of pregnant women in inner city clinics and in 12% of men seen in STD clinics. Incidence is declining due to widespread use of metronidazole for bacterial vaginosis. Transmission is usually through sexual contact though it can rarely be contracted non-venerally. Since it is a sexually transmitted disease (STD), co-infection with other STDs is possible1. It usually infects the vagina and labial area of women and the prostate and urethra of men2.
Clinical Manifestations: In women, trichomonads cause a vulvovaginitis. The signs and symptoms include malodorous, yellow-green, frothy vaginal discharge, dyspareunia, dysuria, lower abdominal discomfort, vulvar erythema, vaginal wall inflammation, and a ‘strawberry cervix’ on direct visualization of the ectocervix. Up to 50% of women seen in STD clinics may be asymptomatic. The protozoa have been recovered from the urethra in 95% of woman with the infection1. The incubation period is 4-28 days2. Although complications from trichomonal vaginitis are rare, it has been associated with premature labor, premature rupture of membranes, and low birth weight during pregnancy. Spread of the organism beyond the lower urogenital tract is rare1.
In men, infection is usually asymptomatic. When symptomatic, it causes urethritis. Trichomonas has been isolated in 5-15% of patients with non-chlamydial non-gonococcal urethritis. Occasionally, it causes epididymitis and superficial penile ulcerations or may involve the prostate.
Laboratory Diagnosis: The differential diagnosis in women includes infection with Gardnerella vaginalis and Candida albicans. Culture is the gold-standard for diagnosis but is impractical clinically due to the need for special media and long incubation time (2-7 days)2. Rapid diagnosis is usually made by a wet mount preparation of fluid collected from the posterior vaginal fornix and placed into a drop of 0.9% saline. The sample should not be taken from the endocervix since this is rarely involved2. Wet mount detects only 50-70% of cases compared with culture but does correlate better with symptomatic infection. Wet mount can detect 50-90% of infections when obtained from the anterior urethra1. Infection can also be detected on slides stained with Wright’s stain or Papanicolaou stain (sensitivity compared with culture 50-60%). Sensitivities compared with culture for other tests include the following: fluorescent immunoassay kits 82-86%; enzyme immunoassays 81-82%; and nucleic acid probes 83%. Rarely, the organism is detected on microscopic examination of urine sediment during urinalysis2.
Treatment: The treatment of choice is the antibiotic metronidazole.
Numerous regimens are employed ranging from a single 2 gram oral dose to
a 500 mg PO bid course for 7 days. Other 5-nitroimidazoles are also used,
especially outside the U.S., including nimorazole, tinidazole, and ornidazole.
The disadvantage of a single dose includes higher re-infection rate if
the patient’s sexual partners are not also treated. Side effects include
mild nausea or bad taste. Concurrent consumption of alcohol may include
vomiting and flusihing1. Single dose metronizdale can be used
to treat trichomoniasis at any stage of pregnancy1. Relative
metronidazole-resistance is an increasing problem. Unfortunately, standardized
methods for determining sensitivity have not been developed. Treatments
for metronidazole-resistant strains have included longer courses of therapy
with the 2 gram oral dose, high-dose metronidazole vaginal cream, and intravenous
metronidazole administration. Other antimicrobials that have been used
include tinidzole and paromomycin1.
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Figure 2: Trichomonas vaginalis, Giemsa stain, 100x oil.3 |
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