Corynebacteria
These organisms are gram-positive aerobic rods of varying length, frequently arranged on smear in sheafs (palisades) or Chinese letter-type configurations. The most important member of this genus is Corynebacterium diphtheriae, which causes diphtheria. Infection usually becomes established in the pharynx. Corynebacterium diphtheriae produces a toxin that affects the heart and peripheral nerves. There is also necrosis of the infected epithelium, with formation of a pseudomembrane of fibrin, necrotic cells, and neutrophils. The disease is now uncommon, but cases appear from time to time, some of them fatal. Contrary to usual belief, the laboratory cannot make the diagnosis from Gram-stained smears. Heat-fixed smears stained with methylene blue are better but, although helpful in demonstrating organisms resembling diphtheria, they still are not reliable enough for definite morphologic diagnosis. Nonpathogenic diphtheroids are normal nasopharyngeal inhabitants and may look very much like C. diphtheriae. To be certain, one must culture the organisms on special Loeffler’s media and do virulence (toxin production) studies. Nevertheless, direct Gram-stained and methylene blue smears are of value, since other causes of pharyngeal inflammation and pseudomembrane formation, such as fungus and Vincent’s angina, can be demonstrated. Therefore, two or three pharyngeal swabs should be obtained, if possible, for smears and for cultures. About 20% of cases will be missed if specimens for culture are not obtained from the nasopharynx as well as the pharynx.
Certain nondiphtheritic species of Corynebacterium are called diphtheroids. These are normal skin and nasopharyngeal inhabitants and appear rather frequently in cultures as contaminants. However, on occasion diphtheroids may produce endocarditis or urinary tract infection, usually in persons with decreased resistance to infection. Various aerobic and anaerobic gram-positive rods such as Propionibacterium, Lactobacillus, and Listeria, morphologically resemble corynebacteria on Gram stain and are frequently included together in the name diphtheroids without being further identified.
Actinomyces
The genus Actinomyces contains several species, of which Actinomyces israelii is the most important. This is a gram-positive filamentous branching bacterium that segments into reproductive bacillary fragments. The organism prefers anaerobic conditions with increased carbon dioxide, but some strains are microaerophilic. Actinomyces israelii produces actinomycosis, a chronic internal abscess-forming infection that characteristically develops sinus tracts to the skin. There typically is a purulent exudate containing small yellow granules, called sulfur granules, which are masses of actinomycetes. Actinomycetes are normal inhabitants of the human oropharynx. Most infections occur in the neck and chest, but infection may occur elsewhere. Several reports indicate a linkage between pelvic infection by A. israelii (which ordinarily is not common) and intrauterine contraceptive devices (IUDs). It has been reported that 5%-10% of asymptomatic IUD users and 40% of IUD users with pelvic infection demonstrate A. israelii on vaginal smear. Culture has not been very successful in isolating the organisms, at least not culture of vaginal specimens. Sulfur granules are rare in vaginal smears. Fluorescent antibody studies on vaginal smears have been more reliable than Papanicolaou cytology smears, although some cytology experts have a high success rate.
Laboratory diagnosis of nonvaginal actinomycosis consists of Gram stain and acid-fast stain on smears of purulent material containing sulfur granules. The granules should be crushed and smeared. Gram-positive filaments without spores could be either actinomycetes or Nocardia asteroides. Nocardia is acid fast, whereas Actinomyces is not. When material for smear or culture is obtained, special precautions should be taken to avoid contamination by normal oropharyngeal or skin bacteria, which may include nonpathogenic Actinomyces species. A. israelii can be cultured under anaerobic conditions using ordinary anaerobic media. If thioglycollate is used, it should be the enriched type and should be incubated in an increased carbon dioxide atmosphere. Rarely, staphylococci or Pseudomonas bacteria may produce infection with formation of sulfur granules, a condition known as botryomycosis.
Actinomyces was originally thought to be a fungus, and actinomycosis has many clinical characteristics of a deep fungal infection. Actinomycosis is often included in the differential diagnosis of fungal diseases.
Nocardia
The genus Nocardia has similarities to Actinomyces, since the members of both genera are gram-positive filamentous branching bacteria that segment into reproductive bacillary fragments. However, Nocardia is aerobic rather than anaerobic, is weakly acid-fast, and usually does not form sulfur granules. The organisms are saprophytes and are found in soil, grasses, grains, straw, and decaying organic matter. The major pathogenic species (80%-90% of Nocardia infections) is Nocardia asteroides. The human infections produced are primary skin lesions (mycetomas), which are very uncommon in the United States, and visceral infections. Of the visceral infections, the lungs are involved in 60%-80% of cases, and the brain is affected in 20%-40%. In the lung, the most common disease produced is focal pneumonia, which often progresses to abscess formation (frequently multiple). However, various x-ray findings have been reported. Pulmonary nocardiosis frequently resembles TB. Occasionally the infection becomes disseminated. There is no preexisting disease in about 25%-35% of cases (range, 15%-71%). About 25% are associated with malignancy (range, 0%-48%). Some series found association with some type of immunosuppression in 50% or more (chronic infection, TB, steroids, diabetes, AIDS, etc.). Nocardia braziliensis is the most common cause of the chronic focal skin and subcutaneous infection known as mycetoma.
Culture is the usual method of diagnosis. The organism grows on various media. However, colonies may take 3 days or more to appear so that cultures on ordinary bacteria media may be discarded before being detected. If cultures are placed on mycobacterial culture media, Nocardia may be mistaken for a rapid-growing nontuberculous Mycobacterium. The weak acid-fast stain reaction may reinforce this impression.
Chlamydiae
Chlamydiae (formerly called bedsoniae) are tiny coccobacillary organisms classified as bacteria because they have a cell wall, are capable of proteinsynthesis, contain both DNA and RNA, and can reproduce by fission. On the other hand, they have some features of a virus in that they are obligate cell parasites, cannot synthesize adenosine triphosphate (ATP), must depend on host cell metabolic processes for energy, and cannot be grown on artificial laboratory media, only in living cells.
There are three species of Chlamydia. One is C. psittaci, the etiologic agent of psittacosis in birds and humans. The second is C. pneumoniae, which causes pharyngitis and pneumonia. The third is C. trachomatis. C. trachomatis includes several serotypes that can be placed into three groups. One group causes lymphogranuloma venereum, a venereal disease. A second group causes the eye disease known as trachoma, and the third group produces genital tract and certain other infections, the genital infections being different from lymphogranuloma venereum.
Chlamydia Psittaci
This produces psittacosis in humans through contact with infected birds, most often parakeets, or as an occupational disease from infected turkeys in the poultry-processing industry. Only a few cases are reported each year in the United States. There are two types of clinical illness: a respiratory type resembling “atypical” pneumonia and a much less common typhoidlike illness. The respiratory type is characterized by headache, chills, fever, and nonproductive or poorly productive cough. There may be myalgias, arthralgias, GI tract symptoms, bradycardia, and changes in mental status. Splenomegaly is found in many patients. The WBC count is normal or slightly decreased. There are various patterns of lung infiltrates on chest x-ray film, although the most typical are patchy lower lobe infiltrates radiating from the hilar areas. Diagnosis can be made by culture, although this is rarely done since tissue culture is required. Diagnosis is usually made by serologic testing of acute- and convalescent-stage serum.
Chlamydia pneumoniae
C. pneumoniae was originally classified as the TWAR strain of C. psittaci but now is a separate species. About 30%-50% (range, 50%-75%) of adults have antibodies derived from previous infection, and C. pneumoniae is said to cause about 10% of pneumoniae and 10%-20% of “primary atypical pneumonia” (pneumonia producing sputum containing WBCs but without bacterial pathogens on standard bacterial culture). This type of pneumonia is similar to that caused by Mycoplasma pneumoniae or Legionella pneumoniae. C. pneumoniae pneumonia is uncommon under age 5 years. Up to 70% of infections are either asymptomatic or afebrile. Some patients react with asthmalike symptoms. Reinfection is said to be common.
Diagnosis is primarily made through serologic tests. Culture can be done but requires a special cell culture line, takes several days, and is relatively insensitive. The basic original serologic test was complement fixation (CF), which is specific for Chlamydia genus but not for species, has sensitivity only about 50%, and usually requires acute and convalescent specimens for definite diagnosis. This was mostly replaced by a specific microimmunofluorescent (MIF) test using antigen from tissue culture. Although little information is available on % MIF sensitivity in C. pneumoniae disease (due to lack of good gold standards), it appears to be substantially more sensitive than culture and might be in the range of 80%-90% of the sensitivity that is obtained in a similar test method used with C. trachomatis infection. At present, this test is available primarily in large reference laboratories or university centers. Specific nucleic acid probes have also been reported and may have even a little better sensitivity than MIF. These too, at present, would need referral to reference or university laboratories.
Chlamydia trachomatis
Lymphogranuloma venereum. Chlamydia trachomatis produces a distinctive venereal disease known as lymphogranuloma venereum, which is transmitted through sexual intercourse. After an incubation period, the inguinal lymph nodes become swollen and tender in males; in females, the lymphatic drainage is usually to the intraabdominal, perirectal, and pelvic lymph nodes. In a considerable number of cases, the perirectal nodes develop abscesses, and the nearby wall of the rectum is involved, eventually leading to scar tissue and constriction of the rectum. In either male or female, in acute stage of lymphatic involvement there may be fever, malaise, headache, and sometimes joint aching, but all of these may be absent. In the majority of cases the main findings are acute inguinal node enlargement in the male and chronic rectal stricture in the female.
Laboratory findings and diagnosis. Laboratory findings in active disease include mild anemia, moderate leukocytosis, and serum protein hypoalbuminemia and hypergammaglobulinemia. On serum protein electrophoresis the gamma-globulin fraction is often considerably elevated without the homogeneous sharp spikelike configuration of monoclonal protein. Similar polyclonal configurations can be found in granulomatous diseases such as TB or sarcoidosis, in some patients with cirrhosis, and in some patients with rheumatoid-collagen disease.
Laboratory diagnosis is usually made through a CF serologic test. The CF reaction becomes positive about 1 month after infection and remains elevated for years. There is also a microimmunofluorescence serologic test that is said to be more sensitive than CF. Acute and convalescent serum specimens should be obtained to demonstrate a rising titer. Relatively low positive CF titers (up to 1:64) may occur in persons with genital tract infections due to serotypes or strains of C. trachomatis that do not cause lymphogranuloma venereum. Also, the test cross-reacts with psittacosis, although this is usually not a problem. It is possible to aspirate affected lymph nodes for culture (although tissue culture is required) and for smears with Giemsa stain or immunofluorescent stains, although reports indicate that positive results are obtained in less than one third of the cases. At one time a skin test known as the Frei test was the mainstay of diagnosis, but the antigen is no longer commercially available. Lymph node biopsy shows a characteristic histologic pattern, which, however, is also seen in tularemia and cat scratch fever. Lymphogranuloma venereum is associated with a relatively high incidence of syphilis serology biologic false positive reactions. This may be difficult to interpret, because syphilis must be suspected in any patient with venereal disease, and early syphilis can produce inguinal lymph node enlargement similar to that caused by lymphogranuloma venereum.
Chlamydial urethritis and endocervicitis. Chlamydia trachomatis can also produce urethral and genital infections that differ clinically from lymphogranuloma venereum and are associated with different organism serotypes. C. trachomatis is reported to cause about 50% (range, 30%-60%) of nongonococcal urethritis in men. Several studies of clinically normal sexually active men not at high risk for venereal disease report asymptomatic chlamydial infection rates of about 10% (range, 5%-26%). About one third of male urethral chlamydial infection is asymptomatic. In some geographic areas or patient populations the incidence of nongonococcal urethritis is two to three times that of gonorrhea. Male patients with gonococcal infection also have chlamydial infection in 20%-30% of cases; and about 70% of cases of postgonococcal urethritis have been attributed to Chlamydia. The urethral discharge in nongonococcal urethritis is usually less purulent than the discharge produced by gonorrhea. C. trachomatis has been found in 40%-50% (range, 6%-69%) of patients with Reiter’s syndrome. Finally, male sexual consorts of women who have chlamydial cervicitis or chlamydial PID are themselves infected by Chlamydia in 25%-50% of cases.
Chlamydiae can infect the female urethra and also the endocervix. Exact incidence in the normal population is unknown, but it has been cultured from the endocervix in about 10% (range, 2%-30%) of asymptomatic women not thought to have venereal disease, 8%-26% of girls attending adolescent clinics, 6%-23% of women attending contraception clinics, in 27%-37% of pregnant female adolescents, and in 10%-48% of women seen in venereal disease clinics. About 60%-80% of infected women are asymptomatic. About 75% of infected women have endocervical infection, about 50% have urethral infection, and about 25% have rectal infection. About 60%-80% of women with cervical infection by Chlamydia are asymptomatic. Patients with PID have a 20%-30% rate of chlamydial recovery from the endocervix and from the fallopian tubes or pelvic abscesses. About 30%-50% of women with gonococcal infections also have chlamydial infection. Chlamydia is also reported to be a major cause for culture-negative female dysuria with frequent urination (acute urethral syndrome), described earlier in this chapter. Finally, female sexual consorts of men who have proven chlamydial urethritis are themselves infected by Chlamydia in up to 70% of cases. If the male consort has gonorrhea, female infection rate for Chlamydia is about 35%; if the male has nongonococcal urethritis, the female will have chlamydial infection in 30%-40% of cases. Chlamydia is now the most common sexually transmitted disease in the United States, causing more infections yearly than all other etiologies combined.
Diagnosis. Diagnosis of C. trachomatis urethritis or cervicitis has been attempted in several ways. Culture (McCoy cell tissue culture) is still considered the gold standard. In males, a thin nasopharyngeal-type calcium alginate swab is inserted 3-4 cm into the urethra. The swab should be rotated for at least 5 seconds and at least one revolution. In females, Chlamydia infects only the columnar and squamocolumnar cervical cells, so that endocervical specimens produce maximum isolation rates, whereas vaginal specimens are not recommended. Therefore cervical culture specimens in the female should be obtained 1-2 cm above the squamocolumnar junction, into the endocervix. The swab should be rotated against the endocervix for 10-30 seconds. Gently cleaning the endocervical canal with a swab before taking the specimen is reported to decrease cell culture contamination and increase positive results. Sensitivity of culture using one swab has varied from 33%-86%. Obtaining two swabs instead of one is reported to increase positive yield from 5%-45%. In one study, an additional urethral culture increased sensitivity by 23%. Swabs with a wooden handle should not be used because the wood contains chemicals that inhibit chlamydiae. Immediately after the specimen is obtained, special transport media should be innoculated with the swabs. The innoculated transport media should be kept at 4°C if culture can be done within 24 hours. If culture cannot be done until after 24 hours, its specimen should be stored at –70°C. Storage in a “frost-free” freezer or at –20°C temperature decreases culture yield. A specimen collection brush (Cytobrush) was claimed to considerably increase the number of columnar cells and thereby increase satisfactory cultures or direct smears in one study but had equal sensitivity to swabs in two other studies. Sensitivity of culture is estimated to be about 80%-90% (range, 63%-97%).
Several manufacturers have marketed kits for direct fluorescent antibody (FA) detection of Chlamydia organisms within infected cells, using the same specimens obtained for culture applied directly to a slide or microtiter wells. This permits same-day results without the delay and many of the technical problems of tissue culture. Only two of these (FA) systems have had reasonably adequate evaluation. Their sensitivity has averaged about 80%-85% (for one of these, the range has been 60%-96%) compared to culture (since culture sensitivity is not 100%, true sensitivity of the FA methods is less than the stated figures). Specificity has averaged 97%-98%.
Some investigators recommend that the direct tests not be used on low-prevalence (<10% incidence) populations, since in that patient group, although the percentage of false positive test results is low, in terms of the number of patients the false positive results become too high. In addition, the percentage of false positive and negative results using FA methods would probably be higher in ordinary laboratories than in research laboratories. Enzyme immunoassay (EIA or ELISA) kits have been replacing FA. Average sensitivity of these EIA kits is about 75%-85% (range, 44%-100%), about the same as FA. One EIA kit evaluation reported detection of over 90% of patients using urine specimens (in males) but only 66% using blood specimens from the same patients. A commercially available DNA probe also has about the same sensitivity (75%-85%; range, 60%-97%). Several nucleic acid probes with PCR amplification have been evaluated; all were more sensitive than culture (about 1.5 times more than culture; range, 1.04-4.5 times). One report indicates that one commercial probe with PCR amplification detected 95% of male urethral chlamydial infections using a urine specimen.
Other chlamydial infections
About 5%-10% (range, 2%-25%) of pregnant women have Chlamydia infestation of the cervix. Fifty percent to 70% of infants born to these infected mothers acquire Chlamydia infection or colonization during birth. Of these, about 30%-50% (range, 18%-75%) develop chlamydial conjunctivitis, with onset about 1-3 weeks after birth; and about 10%-15% (range, 3%-30%) develop chlamydial pneumonia, with onset about 4-12 weeks after birth. In addition, it has been reported that asymptomatic colonization of the vagina, rectum, and pharynx, sometimes lasting over 2 years, may occur in 15% of infected infants. According to some reports, chlamydial infection causes 25%-80% of infant conjunctivitis and about 30% of infant pneumonia. Diagnosis can be made by culture or FA methods from swab material obtained from the posterior nasopharynx, similar to specimens for pertussis. Special transport media are necessary for culture specimens. In possible chlamydial conjunctivitis, culture specimens can be obtained or smears can be made from conjunctival scrapings. Purulent material should be wiped off before scrapings or cultures are obtained since the organisms are found in conjunctival epithelial cells and not in the inflammatory cells of the exudate. Giemsa-stained smears have been used for many years but are difficult to interpret and detect only about 25%-40%.
Trachoma. Finally, C. trachomatis produces trachoma, a serious eye disease that is endemic to North Africa, the Middle East, and Southeast Asia. The conjunctiva is infected and becomes scarred. The cornea is eventually invaded by granulation tissue and is destroyed. Diagnosis usually is made from Giemsa-stained smears of conjunctival scrapings. The infected cells contain cytoplasmic inclusion bodies. However, results of only about one half of the cases are positive. Immunofluorescent techniques applied to the smears produce positive results in about 85% of cases. McCoy cell culture detects about 95% of cases.
Mycoplasma
Mycoplasmas are similar to bacteria in most respects and can be grown on artificial media. However, they lack a cell wall and are smaller than bacteria. There are several genera in the Mycoplasmataceae family. One of these is Ureaplasma, which contains a species, Ureaplasma urealyticum (formerly known as T. mycoplasma) that has been cultured from the urethra of both sexes and cervix or vagina of 40%-80% of clinically normal females. The incidence of positive cultures is increased in persons seen in venereal disease clinics. It is thought that U. urealyticum is an important cause of nongonococcal urethritis in men.
There is accumulating evidence that U. urealyticum can produce placental and fetal infection in obstetrical patients already colonized with the organism. Transmission to the fetus, placenta, or fetal membranes (vertical transmission) is reported to occur in 45%-66% of full-term infants. In most, this results in temporary colonization, with 10% or less of older children still culture-positive. However, in a small number there may be chorioamnionitis, spontaneous abortion, premature birth; less commonly there may be other conditions such as neonatal pneumonia and bronchopulmonary dysplasia. Since maternal colonization is so frequent, this colonization by itself does not predict pregnancy or fetal complications. Diagnosis of infection or suspected infection is usually made by culture. A noncotton swab (or tissue biopsy) should be innoculated directly into special ureoplasma transport medium and the swab then removed. Blood (as much as possible) without anticoagulants can be innoculated into the transport medium in a 1:19 (blood to medium) ratio. Specimen should be refrigerated or kept cold until they enter the laboratory. If the specimen must be sent to a reference laboratory, it should be frozen (at –70°C if possible) and sent frozen.
Another genus has the name of Mycoplasma and contains two species associated with human disease, Mycoplasma hominis and Mycoplasma pneumoniae. Mycoplasma hominis, like U. urealyticum, is a normal inhabitant of the female urethra and female genital organs (20%-40% of persons) and to a lesser degree in the male urethra. In addition, it is occasionally found in the oropharynx of both sexes. The role of M. hominis in nongonococcal urethritis is not clear, but it currently is not thought to produce many cases, if any. There is more evidence for occasional involvement in female PID and occasional infections in immunocompromised patients.
Mycoplasma pneumoniae. Mycoplasma pneumoniae (formerly called Eaton agent, pleuro-pneumonia-like organism) is the most frequent etiologic agent of a lower respiratory tract infection formerly called primary atypical pneumonia (pneumonia with sputum containing neutrophils but no bacterial pathogen cultured). However, Legionella pneumophilia, Chlamydia pneumoniae, and viruses can also produce this syndrome. In one study, Mycoplasma pneumophilia was cultured in 13% of patients with nonstreptococcal acute pharyngitis. Some investigators report that mycoplasma caused 20%-25% of all cases of community-acquired pneumonia in their area. Clinical mycoplasma pneumonia is commonly seen only between the ages of 5-40 years. Patients can be reinfected after 2-10 years. Most cases appear as an upper respiratory infection of varying severity. If pneumonia develops, it is usually preceded by headache, fever, and malaise. Sore throat or chills occur in 30%-50% of patients, and GI symptoms or earache in a lesser number. After 2-4 days there is onset of a nonproductive or poor productive cough. Chest x-ray typically shows lower lobe mottled infiltrates that are most pronounced in the hilar region and that are most often unilateral. However, in some cases other abnormalities develop. Despite the symptoms and chest x-ray findings there is characteristically little abnormality on physical examination.
Laboratory findings and diagnosis. WBC counts are usually normal, although about 25% of affected persons have mild leukocytosis (between 10,000 and 15,000/mm3; 10-15 x 109/L). An unusually severe case may produce more abnormal results. Several modalities are available for diagnosis. Culture can be done using sputum or nasopharyngeal swabs. Mycoplasma pneumoniae is very sensitive to drying, so the swab must be placed immediately in a special transport medium. Special culture media are required, and most laboratories must send the specimen to a reference laboratory. Such specimens should be frozen and transported with dry ice. Growth takes about 2 weeks (range, 1-3 weeks). Compared to CF in various studies, isolation rates from sputum or throat swabs averages about 50%-70% (range, 0%-87%), so that culture does not seem clinically very helpful.
Cold agglutinins are elevated in 50%-60% of patients. Cold agglutinins are antibodies that are able to agglutinate type O human blood cells at refrigerator temperatures but not at room temperature. They are found in other diseases and thus are nonspecific; but in adults with an acute respiratory syndrome, their presence in significant titer is usually associated with mycoplasmal pneumonia. Cold agglutinin titers elevated more than 1:32 are abnormal and can be found during the second week of illness, reaching a peak in the third or fourth week. A rising titer is more significant than a single determination.
Serologic tests are the most common method of diagnosis. Mycoplasmal CF test results are abnormal in 60%-70% of cases (range, 45%-80%). Antibody becomes detectable during the second week of illness and peaks in the fourth week. The CF reaction may become nondetectable after 5-8 years. Immunofluorescent methods for antibody detection are replacing the cumbersome and time-consuming CF technique. Immunofluorescent methods that can detect either IgM or IgG antimycoplasmal antibodies are available (sensitivity 80%-85% compared to CF). The presence of IgM antibodies, especially if present in high titer, usually means acute or recent infection. Immunoglobulin G antibodies rise later than IgM antibodies and persist much longer. It is useful to obtain two serum specimens with a 1-week interval between the first and the second with either IgM or IgG methods. Low levels of mycoplasmal IgG antibodies are very frequent in the general population. Latex agglutination kits are available from several companies; most detect total antibody (IgM plus IgG). Sensitivity varies depending on whether culture or CF tests are used as the gold standard, with reported sensitivity compared to CF about 90% (range, 53%-98%). Finally, one company has marketed a DNA probe method for Mycoplasma that can be applied directly to throat swab specimens, can be performed the same day, and is reported to give 90%-100% correlation with culture. Drawbacks are relatively high cost if only one patient specimen is processed at a time plus a significant but unknown percent of false negative results if detection rates are no better than culture. Other reports have evaluated DNA probes, mostly using home made reagents, which were compared to several different gold standards, thus adding to the variability introduced by different stages of infection and mixes of patients to the variability guaranteed by different antibodies and techniques.
Legionella
Members of this genus are tiny gramegative rods that require special media for culture. They seem to be rather widely distributed and in some cases are linked to water habitats. Most are associated with respiratory tract infection. The predominant species is Legionella pneumophilia; of this species there are two basic types of clinical illness. One is an influenza-like form (sometimes called Pontiac fever), which is nonfatal; and the other is the “primary atypical pneumonia” (classic “Legionnaire’s disease”) form that has been fatal in 10%-20% of cases. Other species have been identified (e.g, Legionella micdadei, the etiology of Pittsburgh pneumonia; see Table 37-9). There is an increased incidence of L. pneumophilia infection in patients who are immunocompromised or have conditions associated with decreased resistance to infection. Spread of infection has most frequently been associated with water in cooling systems.
In the pneumonic Legionnaire’s disease form of illness, there typically is a prodromal stage of 1-10 days with influenza-like symptoms (headache, fatigue, myalgias, and sometimes chills). After this, pneumonia develops with high fever (<103°F; <39.4°C) in approximately 70% or more of cases, recurrent chills in about 70%, nonproductive or poorly productive cough in 50%-80%, pleuritic chest pain in 15%-40%, pleural effusion in 15%-40%, relative bradycardia in approximately 50%, toxic encephalopathy (confusion, disorientation) in 35% or more, and diarrhea in 20%-50%. Laboratory abnormalities include leukocytosis (10,000-30,000/mm3) in 60%-80% of affected persons and mild liver function test elevations in approximately 30%-40%. Proteinuria occurs in about 40% of cases and microscopic hematuria in about 10%. In some series 50% or more of patients had hyponatremia and hypophosphatemia. Radiologically there is pneumonia, which begins unilaterally in 50%-70% of cases, and consists of patchy bronchopneumonia or small densities. This progresses to lobar pneumonia in up to two thirds of patients in some reports, which frequently becomes multilobar and which may become bilateral. Some patients have lobar pneumonia when they are first seen.
Diagnosis is made by culture on special media (not often available in routine laboratories). Although Legionella can be cultured from sputum, there frequently is little sputum produced, and there may be too much contamination by oropharyngeal bacteria. However, one report indicates that rejecting a sputum specimen for Legionella culture on the basis of usual criteria for contamination based on number of squamous epithelial cells or for noninfectivity based on its number of WBCs would result in missing 47%-84% of Legionella culture-positive cases (depending on rejection criteria used). Yield is generally much better from transtracheal aspiration, bronchial washings, pleural fluid, and lung biopsies. Sensitivity of culture presently is about 70% (range, 15%-80%), and the procedure usually takes 3-5 days. Specimens should be kept moist using a small amount of sterile water; saline inhibits growth of Legionella. The specimen should be refrigerated if it cannot be delivered with 30 minutes. Direct fluorescent antibody (DFA) stain on smears prepared from respiratory tract material can be performed in 1-2 hours. However, sensitivity on these specimens is only about 50%-60% (range, 20%-75%). Urine antigen in Legionella disease becomes detectable in 80% of patients at day 1-3 of clinical illness and persists for varying time periods, occasionally as long as a year. Two commercial companies market a latex agglutination kit for urinary antigen (the two kits are apparently identical). In two evaluations, sensitivity was reported to be 54%-92% and specificity was 46%-74%. ELISA methods have been reported to be 70% or more sensitive in detecting urine antigen. Serologic testing (generally by indirect fluorescent antibody methods) is still used, especially for epidemiologic investigation. A fourfold rise in titer to at least 1:128 is diagnostic, and a single titer of at least 1:256 is considered presumptive evidence when combined with appropriate symptoms. However, only about 50% of patients seroconvert by the second week of clinical illness, and it may take 4-6 weeks to obtain maximal rates of seroconversion. Ten percent to 20% of patients do not develop detectable antibodies. Nucleic acid (DNA) probe techniques are beginning to be introduced. At least two of these are said to detect about 67%-74% of cases when applied to respiratory material, which is an increase in sensitivity over DFA. However, DNA probe is expensive and is very expensive when only single specimens are processed.