Utility of complement fixation and microimmunofluorescence assays for detecting serologic responses in patients with clinically diagnosed psittacosis

Challenges in using serological methods to explore historical transmission risk of Chlamydia psittaci in a workforce with high exposure to equine chlamydiosis

Introduction

This report describes the challenges encountered in using serological methods to study the historical transmission risk of C. psittaci from horses to humans.

Methods

In 2017, serology and risk factor questionnaire data from a group of individuals, whose occupations involved close contact with horses, were collected to assess the seroprevalence of antibodies to C. psittaci and identify risk factors associated with previous exposure.

Results

147 participants were enrolled in the study, provided blood samples, and completed a questionnaire. On ELISA testing, antibodies to the Chlamydia genus were detected in samples from 17 participants but further specific species-specific MIF testing did not detect C. psittaci-specific antibodies in any of these samples.

Conclusion

No serological evidence of past C. psittaci transmission from horses to humans was found in this study cohort. There are major challenges in using serological methods to determine the prevalence of C. psittaci exposure.

Clinical features of endemic community-acquired psittacosis

Following a large outbreak of community-acquired psittacosis in 2002 in residents of the Blue Mountains, New South Wales, Australia, we reviewed new cases in this area over a 7-year period from 2003 to 2009. Using the 2010 criteria from the Centers for Disease Control National Notifiable Diseases Surveillance System, 85 patients with possible psittacosis were identified, of which 48 were identified as definite or probable infection. Clinical features of these cases are summarized. In addition to Chlamydia-specific serology, specimens, where available, underwent nucleic acid testing for chlamydial DNA using real-time PCR. Chlamydophila psittaci DNA was detected in samples from 23 patients. Four of 18 specimens were culture positive. This is the first description of endemic psittacosis, and is characterized in this location by community-acquired psittacosis resulting from inadvertent exposure to birds. The disease is likely to be under-diagnosed, and may often be mistaken for gastroenteritis or meningitis given the frequency of non-respiratory symptoms, particularly without a history of contact with birds. Clinical characteristics of endemic and outbreak-associated cases were similar. The nature of exposure, risk factors and reasons for the occurrence of outbreaks of psittacosis require further investigation.

Genetic Diversity and Epizootiology ofChlamydophila psittaciPrevalent among the Captive and Feral Avian Species Based on VD2 Region ofompAGene

To study genetic diversity and occurrence of Chlamydophila psittaci, a total of 1,147 samples from 11 avian orders including 53 genera and 113 species of feral and captive birds were examined using ompA gene based nested PCR. Three types of chlamydiae: C. psittaci (94.12%), C. abortus (4.41%) and unknown Chlamydophila sp. (1.47%) were identified among 68 (5.93%) positive samples (Psittaciformes-59, Ciconiiformes-8 and Passeriformes-1). Based on nucleotide sequence variations in the VD2 region of ompA gene, all 64 detected C. psittaci strains were grouped into 4 genetic clusters. Clusters I, II, III and IV were detected from 57.35%, 19.12%, 10.29% and 7.35% samples respectively. A single strain of unknown Chlamydophila sp. was found phylogenetically intermediate between Chlamydophila species infecting avian and mammalian hosts. Among Psittaciformes, 28 out of 81 tested species including 10 species previously unreported were found to be chlamydiae positive. Chlamydiosis was detected among 8.97% sick and 48.39% dead birds as well 4.43% clinically normal birds. Therefore, it was observed that though various genetically diverse chlamydiae may cause avian chlamydiosis, only a few C. psittaci strains are highly prevalent and frequently associated with clinical/subclinical infections.

Seroprevalence of antibodies to Chlamydophila psittaci in zoo workers in Brazil

To evaluate the prevalence of antibodies to Chlamydophila psittaci 364 serum samples were collected from veterinarians, biologists, animal scientists, veterinary students, animal keepers and others employees in 20 zoos, and from veterinary practitioners in 10 Brazilian states. Subjects ranged from 15 to 64 years of age, with 268 (74%) males and 96 (26%) females. Chlamydial antibodies were determined by the complement fixation test (CFT) and specific anti-C. psittaci IgG antibodies were determined by the microimmunoflurescence (MIF) test. Complement fixation test showed 23.9% (87/364) and MIF test showed 4.7% (17/364) positive serum samples. Titres ranged from 16 to 256 in both assays, demonstrating evidence of recent or current infection. Although chlamydial antibodies were detected in workers of seventeen zoos, MIF test only detected specific C. psittaci antibodies in seven of them. Previous psittacosis infection was suspected in eight workers of two zoos, five of whom reported having pneumonia, while employed at the zoos. However, diagnosis was not established in any of these cases in the past. Results indicated the occurrence of infection and previous contact of Brazilian zoo workers with C. psittaci, as well as the zoonotic potential of psittacosis in this risk population. Other studies are necessary to evaluate the risk factors of infection in this population. This seroepidemiological survey confirmed the need to adopt preventive measures to control avian chlamydiosis and protect the health of zoo workers in the country.

Ornithosis – case report and actual questions

A szerzők egy kritikus állapotú, intenzív osztályon ápolt beteg esetének ismertetése kapcsán foglalják össze az ornithosisdiagnosztika jelenlegi lehetőségeit, epidemiológiai, valamint terápiás vonatkozásait. A kórkép egyéb atípusos bakteriális kórképektől való elkülönítése a klinikai tünetek alapján megbízhatóan nem lehetséges, éppen ezért döntő, olykor életmentő jelentőséggel bír a madárkontaktus felderítése. Az anamnesztikus adatokat rögzítő klinikust mindez egyből a helyes diagnózis felé terelheti, ami az adekvát terápia révén gyors gyógyulást eredményezhet. E bejelentendő kórkép feltehetően mindmáig a gyakran félre- vagy későn diagnosztizált infekciók közé tartozik, így az alulreprezentáltnak tekinthető esetszám nem tükrözi a hazai valós epidemiológiai helyzetet. A szerzők célja, hogy felhívják a figyelmet erre a nem is olyan ritka, ám akár halálos kimenetelű megbetegedésre.

Two fatal cases of psittacosis caused by Chlamydophila psittaci

Two fatal cases of psittacosis are described in two poultry-processing-plant employees presenting with pneumonia and respiratory failure. Diagnosis was confirmed by serological and PCR methods. Psittacosis due to Chlamydophila psittaci infection usually has a good recovery rate, although diagnostic delay and mistreatment can lead to severe complications and even death. This report emphasizes the need for rapid differential diagnosis and management of suspected cases of atypical pneumonia to prevent fatal outcomes.

Development of an internally controlled real-time PCR assay for detection of Chlamydophila psittaci in the LightCycler 2.0 system

A real-time PCR assay with a DNA purification and inhibition control (internal control; IC) was developed to detect Chlamydophila psittaci DNA in human clinical samples. Novel C. psittaci-specific primers targeting the ompA gene were developed. The IC DNA contained the same primer-binding sites and had the same length and nucleotide content as the C. psittaci DNA amplicon, but had a shuffled probe-binding region. The lower limit of detection was 80 target copies/PCR, corresponding to 6,250 copies/mL in a clinical sample. Specificity was tested using reference strains of 30 bacterial species. No amplification was observed from any of these samples. Respiratory samples from eight patients were positive with this PCR. Six of these patients were confirmed as positive for C. psittaci with serological testing. Two patients had increasing antibody titres, but did not fulfil criteria proposed previously for serologically proven Chlamydia spp. infection. The real-time PCR described in this paper is a sensitive, specific and rapid method to detect C. psittaci DNA in human clinical respiratory samples.

Multiplexed serology in atypical bacterial pneumonia

Atypical pneumonia is a term applied to lower respiratory tract infections that are not characterized by signs and symptoms of lobar consolidation. This article will discuss the epidemiology, clinical manifestations, and laboratory diagnoses of Mycoplasma pneumoniae, Chlamydia sp., Legionella sp., Francisella tularensis, and Coxiella burnetii, which are the agents most commonly associated with atypical pneumonia. Because many of these pathogens are intracellular, diagnosis depends upon serological confirmation. The current serological tests used to identify these agents in the etiologic diagnosis of atypical pneumonia are described. Recently, however, it has become possible to make a diagnosis directly in these cases using DNA or protein microarrays. Here, we describe the development of a new, automated technique for simultaneous testing and detection of several pathogens using a multiplexed serology test. This should prove to be a valuable tool for the rapid determination of patient status, allowing effective and efficient postexposure prophylaxis and treatment.

An outbreak of psittacosis due to Chlamydophila psittaci genotype A in a veterinary teaching hospital

An outbreak of psittacosis in a veterinary teaching hospital was recognized in December 2004. Outbreak management was instituted to evaluate the extent of the outbreak and to determine the avian source. Real-time PCR, serologic testing and sequencing of the ompA gene of Chlamydophila psittaci were performed. Sputum samples from patients, throat-swab samples from exposed students and staff, and faecal specimens from parrots and pigeons were tested. In this outbreak, 34 % (10/29) of the tested individuals were infected. The clinical features of the infection ranged from none to sepsis with multi-organ failure requiring intensive-care-unit admission. C. psittaci genotype A was identified as the outbreak strain. Parrots, recently exposed to a group of cockatiels coming from outside the teaching facility, which were used in a practical class, appeared to be the source of the outbreak. One of the tested pigeons harboured an unrelated C. psittaci genotype B strain. The microbiological diagnosis by real-time PCR on clinical specimens allowed for rapid outbreak management; subsequent genotyping of the isolates identified the avian source. Recommendations are made to reduce the incidence and extent of future outbreaks.

Probable psittacosis outbreak linked to wild birds

Residence in the upper Blue Mountains, age of 50–64 years, direct contact with wild birds, and lawn mowing without a grass catcher were associated with psittacosis.

In autumn 2002, an outbreak of probable psittacosis occurred among residents of the Blue Mountains district, Australia. We conducted a case-control study to determine independent risk factors for psittacosis by comparing exposures between hospitalized patients and other residents selected randomly from the telephone directory. Of the 59 case-patients with laboratory results supportive of psittacosis, 48 participated in a case-control study with 310 controls. Independent risk factors were residence in the upper Blue Mountains (odds ratio [OR] = 15.2, 95% confidence interval [CI] 5.6–41.7), age of 50–64 years (OR = 3.9, 95% CI 1.5–10.5), direct contact with wild birds (OR = 7.4, 95% CI 2.5–22), and mowing lawns without a grass catcher (OR = 3.2, 95% CI 1.3–8.0). Protective equipment is recommended for residents in areas frequented by free-ranging birds if contact with birds and their droppings is likely when performing outdoor activities such as lawn mowing.

ELISPOT assay for Chlamydia-specific, antibody-producing cells correlated with conventional complement fixation and microimmunofluorescence

Chlamydia antigens cross-reactive with pneumoniae (TWAR), psittaci, and trachomatis strains were used to evaluate the ELISPOT assay for detecting antigen-specific, antibody-secreting cells (ASC). Human blood specimens from healthy and hospitalized persons were randomly collected and tested by coating the nitrocellulose membrane at the base of microtiter wells. Ficoll-separated mononuclear cells from blood specimens collected in EDTA were incubated in the wells with Iscove's growth medium in CO2 atmosphere at 37 degrees C. An IgG-specific conjugate labeled with biotin was used in an avidin-peroxidase chromogen system for indicating the areas (spots) of immunologically committed lymphocytes. Positive specimens had median levels of ASC above 8 per 10(6) cells (range 15-23 ASC/10(6) cells). Evidence that the ELISPOT is reliable, sensitive, and specific includes the following:(1) immunized animal and clinical human specimens in control experiments were selectively reactive in the presence of antigen, but negative without antigen, (2) serologically characterized reference sera demonstrated homologous rather than heterologous reactions with the antigens, (3) conventional complement fixation and microimmunofluorescence on serum fractions of clinical specimens correlated well (P < 0.02) with ELISPOT results that were both TWAR- and psittaci-positive, and (4) the array of specimens (from healthy donors, community hospitalized, and pulmonary service patients) selected for their increasing likelihood in that order for being positive due to illness was then confirmed and supported by their respectively increasing positivity rates (6, 15, and 25%) for TWAR/psittaci combined. The incidence of positive specimens for either TWAR or psittaci was greatest (23/54, 43%) in specimens from the hospitalized patients and least (8/33, 24%) in specimens from healthy individuals. These findings suggest that ELISPOT detects chalmydial antibody production at the cellular level. ELISPOT positivity thus indicates previous exposure and would favor earlier detection.

Lack of association between Kawasaki syndrome and Chlamydia pneumoniae infection: an investigation of a Kawasaki syndrome cluster in San Diego County

BACKGROUND

The etiology of Kawasaki syndrome (KS), the leading cause of acquired coronary artery disease in children, is unknown. Recent studies have suggested that Chlamydia pneumoniae, a common respiratory pathogen associated with an increased risk of heart disease, might lead to KS.

OBJECTIVE

To assess whether KS was associated with an elevated risk of having a current or antecedent infection with C. pneumoniae.

METHODS

Blood, urine and pharyngeal specimens from KS patients in San Diego County, CA, during a period of high KS incidence were analyzed for evidence of recent C. pneumoniae infection by culture, PCR and serology. Specimens collected from two control groups, family members of KS patients and age-matched children attending outpatient clinics for well child visits, were similarly analyzed.

RESULTS

Thirteen cases were identified. Forty-five outpatient controls and an average of three family members per patient were enrolled in the study. All specimens tested negative for the presence of C. pneumoniae by PCR and culture except for one blood specimen from the mother of a case-patient. Serologic analysis of patients and a subset of outpatient and family controls revealed no evidence of current C. pneumoniae infection; 4 of 13 adult family controls had IgG titers consistent with past exposure to C. pneumoniae. Case patients were no more likely than outpatient controls to have had a respiratory illness in the preceding 2 months (11 of 13 patients vs. 35 of 45 controls; odds ratio, 1.57; 95% confidence interval, 0.3 to 11.9).

CONCLUSIONS

We found no evidence that C. pneumoniae infection was associated with KS.

Fulminant psittacosis requiring mechanical ventilation and demonstrating serological cross-reactivity between Legionella longbeachae and Chlamydia psittaci

Chlamydia psittaci infection typically causes a mild respiratory illness in humans. Severe respiratory failure requiring mechanical ventilation or intensive care therapy is an uncommon development. The aetiological agents causing severe community acquired pneumonia often remain undetermined. Serological tests may aid in diagnosis. We present two cases of fulminant psittacosis, one demonstrating early cross-reactivity with Legionella longbeachae.

How useful is the Chlamydia micro-immunofluorescence (MIF) test for the gynaecologist?

Three patients with a chlamydial respiratory tract infection showed significant titre rises for the three chlamydial micro-immunofluorescence tests, performed with Chlamydia pneumoniae, C. psittaci and C. trachomatis. Such cross-reactions procure an inaccurate discrimination between the various Chlamydia species which remains speculative anyhow when only a positive serological profile against one chlamydial subspecies is performed. We consider that using the serologic assay as proof for past sexually transmitted C. trachomatis infection falls outside the limits of prudent interpretation of laboratory tests.

ELISPOT assay for Chlamydia-specific, antibody-producing cells correlated with conventional complement fixation and microimmunofluorescence

Chlamydia antigens cross-reactive with pneumoniae (TWAR), psittaci, and trachomatis strains were used to evaluate the ELISPOT assay for detecting antigen-specific, antibody-secreting cells (ASC). Human blood specimens from healthy and hospitalized persons were randomly collected and tested by coating the nitrocellulose membrane at the base of microtiter wells. Ficoll-separated mononuclear cells from blood specimens collected in EDTA were incubated in the wells with Iscove's growth medium in CO2 atmosphere at 37 degrees C. An IgG-specific conjugate labeled with biotin was used in an avidin-peroxidase chromogen system for indicating the areas (spots) of immunologically committed lymphocytes. Positive specimens had median levels of ASC above 8 per 10(6) cells (range 15-23 ASC/10(6) cells). Evidence that the ELISPOT is reliable, sensitive, and specific includes the following:(1) immunized animal and clinical human specimens in control experiments were selectively reactive in the presence of antigen, but negative without antigen, (2) serologically characterized reference sera demonstrated homologous rather than heterologous reactions with the antigens, (3) conventional complement fixation and microimmunofluorescence on serum fractions of clinical specimens correlated well (P < 0.02) with ELISPOT results that were both TWAR- and psittaci-positive, and (4) the array of specimens (from healthy donors, community hospitalized, and pulmonary service patients) selected for their increasing likelihood in that order for being positive due to illness was then confirmed and supported by their respectively increasing positivity rates (6, 15, and 25%) for TWAR/psittaci combined. The incidence of positive specimens for either TWAR or psittaci was greatest (23/54, 43%) in specimens from the hospitalized patients and least (8/33, 24%) in specimens from healthy individuals. These findings suggest that ELISPOT detects chalmydial antibody production at the cellular level. ELISPOT positivity thus indicates previous exposure and would favor earlier detection.

Chlamydia DNA extraction for use in PCR: stability and sensitivity in detection

We evaluated multiple procedures for extracting chlamydial DNA from specimens for detection in PCR tests. Commercial kits and an in-house method were tested for their sensitivity and utility. Quantifiable chlamydial elementary bodies (EB) were used for spiking buffy coats from EDTA-collected blood. EBs of Chlamydia pneumoniae at 2,500 and 25 EB/ml were used as specimens for DNA extraction using seven different procedures. These included either columns (3 procedures), centrifugation (1), glass (1), or patented extraction matrices (2), coupled with either alcohol precipitation (6) or heat-detergent treatment (1). Five procedures required 10-40 minutes manipulation; two required 2-5 hours. PCR results for DNA extracts using chlamydial 16S genus primers were generally more intensely positive with denser bands on electrophoresis gels for the higher concentrations of EB (up to 4+ for stained product on gels) than was PCR with lower EB concentrations (up to 2+). Further, the incidence of procedures with positive results was: 5 of 7 for chlamydial genus primers with 5 EB vs. 6 of 7 with 500 EB. Maximal sensitivity for one of the extractions was in the range of 2.5-5.0 EB/ml of test specimen with 4 of 5 replicates being positive with EB controls or extracts. Extracts were stable up to 2+ weeks at 4 degrees C and were effective in multiplexing with fluorescent-tagged primers. Taking into consideration the time factor and sensitivities, the two procedures with extraction matrices are favored for routine laboratory use.

Psittacosis. Is contact with birds causing your patient's pneumonia?

Psittacosis is an uncommon source of community-acquired pneumonia but can cause significant morbidity and possibly death if not properly diagnosed and treated. Although it occurs most often among handlers of pet psittacine birds, it can be contracted during poultry processing and other contacts with nonpsittacine birds. Clinical presentation is nonspecific, and history taking is often critical in establishing the diagnosis. All suspected cases should be confirmed with serologic antibody testing. Whenever possible, the source of the infection should be identified to prevent further spread of the illness. Infections in humans should be reported to the CDC.

Application of a nested, multiplex PCR to psittacosis outbreaks

We developed a nested, multiplex PCR for simultaneous detection of three species of chlamydiae in human and avian specimens. The PCR was designed to increase sensitivity and to circumvent inhibitors of PCR present in clinical specimens. The target sequence was the 16S rRNA gene. The first-step PCR was genus specific, and the second-step PCR was multiplexed (i.e., had multiple primer sets in the same tube) and could discriminate among Chlamydia pneumoniae, Chlamydia psittaci, and Chlamydia trachomatis on the basis of the molecular weight of the amplicon. The limit of detection of each of the two PCR steps was 5 inclusion-forming units. We used PCR and serologic evidence during outbreaks of psittacosis to infer that C. psittaci had been transmitted from birds purchased in pet stores to humans. We also used this method to test both live and dead birds from pet stores for infection with C. psittaci. Compared with culture, the application of PCR to avian specimens increased the rate of C. psittaci detection.

Psittacosis in Egypt: A Case Study

Psittacosis, also referred to as ornithosis, is a disease primarily of birds, which may be transmitted to humans. Psittacosis is caused by Chlamydia psittaci, an obligate intracellular parasite found worldwide. Humans are infected with C. psittaci when the organism enters the blood stream, usually through inhalation of dried excrement from diseased birds or through wound contamination with infected avian secretions. C. psittaci replicates in the liver and spleen and infects the lung and other organs hematogenously.1 The clinical manifestations of human psittacosis range from a mild respiratory infection to a severe systemic illness.1,2 Symptoms are frequently described as flu-like with fever, headache, body aches, and dry or productive cough. Sore throat, chest pain, abdominal pain, vomiting, and diarrhea are variably present. Physical findings may include a pulse-temperature dissociation, localized lung crackles, hepatomegaly, splenomegaly, and a pale macular skin rash. Chest radiographs may demonstrate lesions that are atelectatic, patchy, miliary, nodular, or consolidated in one or both lungs. White cell counts, erythrocyte sedimentation rates, and liver function tests are usually normal. In severe illness, signs and symptoms of liver dysfunction, neurological impairment, and respiratory and renal failure may be present. Since 1879 when psittacosis was recognized as a disease entity, cases have been reported in North and South America, Europe, Asia, and Australia. However, reports of psittacosis in Africa have been rare. An Ethiopian group, studying community-acquired pneumonia, published what they claimed to be the first report of psittacosis in Africa in 1994.3 The report published here is believed to be the first documented case of human psittacosis in Egypt.

Atypical respiratory pathogens

The main atypical pathogens in respiratory tract infections are classified on the basis of their ability to cause atypical pneumonia. This is not a well-defined clinical entity, and it is evident that atypical pathogens can sometimes cause 'typical' pneumonias and vice versa. This emphasizes the need for microbiological diagnosis, since it affects the selection of proper treatment, in which beta-lactam antibiotics and aminoglycosides are not effective. Moreover, mixed infections caused by atypical and typical pathogens together are common. At this moment rapid and sensitive diagnostic methods are lacking. Besides numerous viruses, the main bacterial pathogens causing atypical pneumonias are Mycoplasma pneumoniae, two chlamydial species, Chlamydia pneumoniae and C. psittaci, one rickettsia, Coxiella burnetti, and several Legionella species. The majority of these pathogens cause upper respiratory tract infections more often than overt pneumonias. An atypical agent, Chlamydia pneumoniae, has also been associated with chronic inflammatory conditions in the cardiovascular system. The most recently discovered pathogen in atypical pneumonias is a hantavirus causing hantavirus pulmonary syndrome.

Myopericarditis due to Chlamydia psittaci. The role of autoimmunity

Chlamydia psittaci may rarely involve the heart as the only manifestation of the infection. We report a case of myopericarditis caused by this agent, whose pathogenesis seemed to be autoimmune damage triggered by the infection.

Prevalence of Chlamydia trachomatis, Chlamydia psittaci and Chlamydia pneumoniae antibodies in blood donors and attendees of STD clinics

OBJECTIVE: To estimate the prevalence of Chlamydia trachomatis, C. psittaci and C. pneumoniae antibodies in sera from altogether 931 blood donors, patients with symptoms of urethritis, assumed salpingitis and sexually acquired reactive arthritis (SARA), and women with fertility problems. METHODS: IgG antibodies to C. trachomatis, C. psittaci and C. pneumoniae were determined by microimmunofluorescence (MIF) tests. All patients were also tested for genital C. trachomatis infection using direct immunofluorescence (DIF) tests. RESULTS: The DIF-positive cases had a significantly (p < 0.0001) higher prevalence of C. trachomatis antibodies than the DIF negatives, i.e. 88.5% versus 14% in men with urethritis, 94.3% versus 36.4% in women with salpingitis, 66.7% versus 16.7% in SARA patients and 90.6% versus 20.8% in women with fertility problems. Antibody reactivity to all three chlamydial species was found significantly (p < 0.0001) more often in the patient groups and in those with a DIF-confirmed genital C. trachomatis infection than in blood donors. CONCLUSIONS: Presence of serum antibodies to C. trachomatis is tightly associated with the presence of chlamydiae in the genital tract, which also influences the cross-reactivities occurring in the MIF tests between chlamydial species.

A seroepidemiologic study of Chlamydia pneumoniae, Chlamydia trachomatis and Chlamydia psittaci in different populations on the mainland of China

To evaluate and compare the prevalence of antibodies to 3 chlamydial species in various populations on the mainland of China, the MIF test was used to detect both serum IgG and IgM antibodies to these species in the normal population (n = 711), in poultry workers (n = 51), in female prostitutes (n = 106), in patients attending the sexually transmitted diseases clinic (n = 98), and in adult patients with pneumonia and bronchitis (n = 108). In the normal population, IgG antibodies against C. pneumoniae, C. trachomatis and C. psittaci were present in 61.5%, 9.3%, and 3.5%, respectively, and increasing with age. Prevalence and geometric mean titers (GMT) of IgG antibodies to C. trachomatis in prostitutes (54.7%) and female (55%), but not male (15.4%) sexually transmitted disease patients were significantly higher than in the normal adult female population. The prevalence indicating both previous and recent C. psittaci infections in poultry workers was no higher than in the others. The prevalence of IgG antibodies and GMT to C. pneumoniae in patients with pneumonia and bronchitis was not statistically higher than in the normal adult population. Evidence of cross-reactivities in the MIF test between different species was found in both prevalence and GMT. Serum IgM antibodies were usually absent in patients who met the serological criteria of recent C. pneumoniae infection, indicating that most of them could be considered as reinfections. On the basis of our survey, acute antibodies to C. pneumoniae by the MIF test, if they are detected, may be valuable in the diagnosis of recent C. pneumoniae infections.