Prostatitis as initial manifestation of Chlamydia psittaci pneumonia diagnosed by metagenome next-generation sequencing: A case report

Abstract Chlamydia psittaci (C. psittaci) pneumonia is a zoonotic infectious disease caused by C. psittaci, which is often underdiagnosed. The application of metagenomic next-generation sequencing (mNGS) provides an unbiased method for the detection of unknown pathogens. A 46-year-old man received empirical treatment with piperacillin-tazobactam and moxifloxacin after an initial diagnosis of prostatitis and pneumonia. However, he experienced recurrent symptoms and a cough, and a chest computed tomography (CT) showed aggravated pulmonary inflammation. Upon further questioning, the patient recalled a history of contact with pigeons, and a bronchoscope alveolar lavage fluid analysis with mNGS suggested C. psittaci infection. Following treatment with doxycycline, the patient’s symptoms were rapidly alleviated, and chest CT showed pulmonary lesions absorption. The patient was followed up for 1 month without any discomfort. This case highlights that initial manifestations of C. psittaci pneumonia may present with atypical symptoms such as prostatitis. Furthermore, mNGS can be a useful tool for the detection of rare or unknown pathogens such as C. psittaci.


Background
Chlamydia psittaci (C. psittaci) is a Gram-negative chlamydia that can infect a wide range of hosts, primarily transmitted via respiratory secretions and feces of birds, including parrots, pigeons, gulls, and other poultry or wild birds [1,2]. Many outbreaks of C. psittaci infection in humans, also known as psittacosis, have been reported worldwide [3][4][5], while sporadic cases have been reported now and then in Asia [6]. Psittacosis in humans is a nationally notifiable disease required by US Centers for Disease Control [7]. Zoonotic transmission of C. psittaci infection can cause various illness, ranging from subtle symptoms to severe systematic diseases, mainly affecting the lungs [8]. C. psittaci pneumonia is a disease resulting from C. psittaci infection, and the proportion of community-acquired pneumonia (CAP) due to C. psittaci is estimated to range from 0 to 6.7% [9]. The onset of C. psittaci pneumonia usually follows an incubation period of 5-14 days, which also can be several weeks, while symptomatic infections usually present with typical symptoms including fever, headache, cough, and chest distress [10].
Case reports of C. psittaci pneumonia have increased in recent years. However, asymptomatic infection or the absence of typical symptoms at onset may lead to undiagnosed infections, resulting in delayed or inadequate treatment. Therefore, it is essential to report and discuss cases with atypical initial manifestations that are eventually diagnosed as C. psittaci pneumonia to raise clinical awareness of atypical CAP and promote disease management. The metagenomic next-generation sequencing (mNGS) shows great favorability in detecting pathogens that are evasive, fastidious, and/or pose a transmission risk using conventional methods. Herein, we reported a case of C. psittaci pneumonia with prostatitis as the initial manifestation for the first time, which was diagnosed using mNGS. symptoms and febrile sickness. He had experienced frequent micturition and urgency, painful urination, dysuria, and discomfort of perineal swelling for about a week before admission, but did not seek medical attention. The patient reported no other symptoms such as nausea, vomiting, cough, sputum expectoration, dyspnea, fever, chills, and other discomforts. As fever occurred with a temperature of 38.5°C and lasted for 1 day without any chills and cough, he presented to the fever clinic and was referred to the urology department. The patient had no history of major diseases or infectious diseases, except for an allergy to sulfonamides. He had a smoking history of 30 cigarettes per day for 25 years and drank alcohol occasionally. On admission, his vital signs included temperature (T) of 38.7°C, pulse (P) of 92 beats/min and respiration (R) of 20 times/min, and blood pressure (Bp) of 150/90 mmHg. Pulmonary auscultation suggested that rough breath sounds in both lungs, while rhonchi and crackles were not heard. The left renal area was tender to percussion, and a digital rectal examination revealed prostate tenderness. Other physical examination results were unremarkable. Chest computed tomography (CT) scan showed double pneumonia and bilateral localized thickening (Figure 1a). Laboratory examinations of blood, urine, and prostatic fluid were performed after admission, and the results are shown in Table 1. B-Scan ultrasonography of the urinary system showed multiple small calculi in both kidneys. Considering the medical history and current examination results, prostatitis, pneumonia, and kidney calculi were tentative diagnoses. The patient was administered piperacillin-tazobactam (4.5 mg, intravenous (IV) injection, quaque 8 hours) for anti-infective treatment and symptomatic treatment for spasmolysis and relaxation of urethral smooth muscle.
After initial treatment, the patient's fever did not abate. On April 22, 2021, a consultation with the department of Respiratory and Critical Care Medicine confirmed the diagnosis of CAP and considered the possibility of mycoplasma infection. Empirical treatment with antimicrobial moxifloxacin (0.4 g, IV, quaque die) and antiviral agent oseltamivir (75 mg, peros, bis in die) was initiated, which gradually alleviated the patient's symptoms of painful urination and dysuria, and brought his body temperature back to normal within 2 days. However, on April 28, 2021, the patient developed a fever again (T, 38.5°C) along with cough, mild chest tightness, and breathlessness. Re-examination of chest CT showed double pneumonia with localized thickening of bilateral pleura, with increased range of flocculent high-density shadow in lobes of bilateral pulmonary as compared to the initial examination ( Figure 1b). After reconsultation, the patient was transferred to the department of Respiratory and Critical Care Medicine for further treatment.
After a detailed medical history investigation, the patient recalled having killed over 10 pigeons approximately 2 weeks before. Considering the possibility of C. psittaci pneumonia, electronic bronchoscopy was performed for etiological evidence, but no obvious abnormalities were noticed in the trachea and bronchus. Bronchoalveolar lavage (BAL) was performed, and bronchoalveolar lavage fluid (BALF) was collected for examination. Microbiological examination of BALF revealed a small number of Gram-positive cocci and Gram-negative bacilli. No fungi were found in BALF, while (1,3)-β-D-glucan (BDG) test (G test) and galactomannan antigen test (GM test) were negative. Routine blood examination ( Table 1) showed that procalcitonin was within normal range; plasma albumin value was below the normal range, but there were no abnormalities in blood potassium, blood sodium, blood chloride, liver function, and renal function. Antibodies of mycoplasma, chlamydia, EB virus, and blood tuberculosis were all negative. Two weeks later, the chlamydia antibody was positive, and its negative may be related to the short time. BALF analysis with mNGS (Simcere Diagnostic, Nanjing, China) reported sequence reads of Burkholderia contaminans complex (3488), Stenotrophomonas maltophilia (145), Pseudomonas aeruginosa (22), Candida albicans (441), Aspergillus flavus (4), and C. psittaci (13) (Figure 2). The number of C. psittaci sequences detected by mNGS in the patient's prostate fluid was 7. By joint consideration of the patient's history of close contact with pigeons and C. psittaci infection suggested by mNGS, the diagnosis of C. psittaci pneumonia was confirmed. On May 1, 2021, doxycycline (100 mg, IV, quaque 12 hours) was administered in combination with moxifloxacin, and the fever subsided the next day. After 5 days, a re-examination of chest CT revealed that lesions were mostly absorbed and pneumonia was significantly improved (Figure 1c). After doxycycline combined with moxifloxacin treatment, the fever did not recur, respiratory symptoms subsided, and the urinary system symptoms alleviated significantly. Due to improvement, the patient was discharged on May 10, 2021. Regarding bilateral kidney calculi, he was instructed to drink plenty of water and consulted the department of urology if necessary. With a follow-up for 1 month, the patient did not have any discomfort. The disease progression of the patient and treatment procedure are shown in Figure 3.
Informed consent: Informed consent has been obtained from all individuals included in this study.
Ethical approval: The research related to human use has been complied with all the relevant national regulations, institutional policies and in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors' institutional review board or equivalent committee.

Discussion
The clinical manifestations of C. psittaci pneumonia vary from asymptomatic in mild cases to multiple organ failure in severe cases [11]. The atypical clinical manifestations of C. psittaci pneumonia may be related to the special infection mode. C. psittaci infection occurs through inhalation of excretion aerosol from birds or other infectious sources, which leads to the pathogen's proliferation in reticuloendothelial cells of the liver and spleen via blood circulation, eventually affecting the lungs and possibly leading to systemic infection [8]. Previous cases have reported pneumonia with other systemic organ diseases including splenomegaly, myocarditis, keratitis, gastrointestinal symptoms, and even fatal meningitis [10,12]. To our knowledge, this is the first report of prostatitis as the initial manifestation of C. psittaci pneumonia. Although prostatitis is common in male patients under 50 years, its  etiology is still unclear, with pathogenic factors typically including infection by a pathogen [13]. In this case, no significant abnormalities were found in routine urine tests, thus excluding urinary tract infection as a possible cause. Based on initial chest CT findings of lung inflammation and increased white blood cell count in prostatic fluid, diagnoses of pneumonia and prostatitis were made. Initially, C. psittaci infection was not suspected due to the lack of relevant evidence, and empirical anti-infective agents were used. However, worsening symptoms of diffuse pulmonary inflammatory lesions shown by chest CT after initial treatment suggested that the pathogen might not be common.
In the initial examination of chest CT examination, nodules were observed in the upper lobes of the lungs, distributed along the pleura, and accompanied by a slight halo sign. However, misdiagnosis as mycoplasma infection resulted in the progression of flocculent highdensity shadow increased in the leaves of bilateral pulmonary and diffusion of peripheral halo. Notably, the upper lobe of the left lung showed ground-glass opacity, indicating the development of the disease. There is limited literature available on the imaging changes associated with C. psittaci pneumonia. While a comparative study reports ground-glass opacity as the most common imaging change [14], others have attached importance to lobar consolidation [15]. Some scholars suggest that the halo sign is a typical imaging change of this disease [16], whereas we think that the halo sign is not a specific change and can be observed in a variety of diseases such as pulmonary cryptococcosis [17]. Due to a lack of specificity in imaging, the differential diagnosis requires the identification of a variety of atypical pneumonia, including Coxiella burnetii, Legionella, Chlamydia, and Mycoplasma [18]. Despite considering the possibility of fungal infection, BALF smear, G test, and GM test showed no abnormalities.
Clinical diagnosis of C. psittaci pneumonia can be challenging due to the nonspecific imaging findings and patient symptoms. Traditionally, psittacosis is diagnosed based on clinical presentation, culture, and serological tests, which include complement fixation (CF), microimmunofluorescence (MIF), or enzyme(−linked) immunosorbent assay (ELISA). However, these methods can be ambiguous and deceptive due to cross-reactivity with other species, and culture is often used to confirm the results of serological tests [19]. Molecular tests, such as polymerase chain reaction (PCR), have become more popular due to their sensitivity and specificity for targeted detection [10], replacing serological methods in some cases. However, these methods require a predetermined assumption of pathogen target, which may lead to missing rare pathogens. In this case, the patient did not report a history of contact with pigeons at admission; meanwhile, we neglected the occupational characteristics of the patient as a farmer and did not pay attention to the possibility of Chlamydia infection, resulting in an aggravation of the patient's condition. C. psittaci infection suggested by mNGS provided guidance for final diagnosis and effective treatment. mNGS can characterize all DNA or RNA existing in the samples and construct the isolated DNA and RNA libraries, so as to analyze the human host genome or transcripts in the whole microbial group and patient samples [20]. The advantage of mNGS is that it can detect any part of the genome unbiasedly to quickly identify potential pathogens, especially rare ones. The patient may not have been clearly diagnosed in this case if we did not perform mNGS. Reports of C. psittaci pneumonia detected by mNGS have increased gradually in recent years [12,21,22]. But it also has drawbacks. In addition to expensive and time-consuming deficiencies, not all genomes suggested by mNGS are available. Other limitations include host genomic predominance of sequence reads in patient samples (reduces sensitivity) and lower clinical utility. In the present case, counting of sequence reads Burkholderia contaminans complex and Candida albicans were much higher than that of C. psittaci, but Burkholderia contaminans had a limited effect on doxycycline and moxifloxacin, and this patient had an excellent effect on doxycycline, confirming the unlikelihood of Burkholderia contaminans infection. The number of C. psittaci sequence detected by mNGS of prostatic fluid was 7, and we finally established the diagnosis of C. psittaci pneumonia based on the patient's history of pigeon exposure. Overall, mNGS is a novel technique that facilitates the diagnosis of unknown pathogens, but its data still need to be interpreted in conjunction with clinical interpretation and clinical standardization is also necessary.
During the therapy procedure, piperacillin-tazobactam was used for initial treatment, which is a typical antibiotic regimen for acute bacterial prostatitis [23]. However, since the patient's symptoms did not improve, moxifloxacin was administered. Moxifloxacin, as a fourth-generation fluoroquinolone, has a broad spectrum of efficacy against Gram-positive bacteria and atypical pathogens, such as Mycoplasma and Chlamydia [24]. However, moxifloxacin alone is less effective in treating C. psittaci pneumonia, as demonstrated by the continued disease progression in this case, despite its reported effectiveness [12]. The recommended first-line treatment for C. psittaci pneumonia is tetracycline antimicrobials, such as doxycycline, while macrolide antimicrobials are considered an alternative for patients who are contraindicated with tetracyclines [10]. After C. psittaci infection was detected by mNGS and treatment with doxycycline combined with moxifloxacin, patient's condition was obviously controlled and the imaging also showed obvious absorption of the lesions in this case. Doxycycline combined with moxifloxacin in the treatment of C. psittaci pneumonia has been reported in some cases [12,21], but it is not clear whether the combination is more effective than the single drug, and further research is needed.

Conclusions
C. psittaci pneumonia may present with atypical symptoms such as prostatitis. In cases where the initial empirical antiinfective therapy for atypical CAP is ineffective, mNGS is a promising method for identifying the pathogen and providing guidance for precise clinical treatment.