Comparison of serological tests for detection of immunoglobulin M antibodies to Chlamydophila pneumoniae

Aetiological agents of adult community-acquired pneumonia in Japan: systematic review and meta-analysis of published data

OBJECTIVE

Epidemiological information is essential in providing appropriate empiric antimicrobial therapy for pneumonia. This study aimed to clarify the epidemiology of community-acquired pneumonia (CAP) by conducting a systematic review of published studies in Japan.

DESIGN

Systematic review.

DATA SOURCE

PubMed and Ichushi web database (January 1970 to October 2022).

ELIGIBILITY CRITERIA

Clinical studies describing pathogenic micro-organisms in CAP written in English or Japanese, excluding studies on pneumonia other than adult CAP, investigations limited to specific pathogens and case reports.

DATA EXTRACTION AND SYNTHESIS

Patient setting (inpatient vs outpatient), number of patients, concordance with the CAP guidelines, diagnostic criteria and methods for diagnosing pneumonia pathogens as well as the numbers of each isolate. A meta-analysis of various situations was performed to measure the frequency of each aetiological agent.

RESULTS

Fifty-six studies were included and 17 095 cases of CAP were identified. Pathogens were undetectable in 44.1% (95% CI 39.7% to 48.5%). Streptococcus pneumoniae was the most common cause of CAP requiring hospitalisation or outpatient care (20.0% (95% CI 17.2% to 22.8%)), followed by Haemophilus influenzae (10.8% (95% CI 7.3% to 14.3%)) and Mycoplasma pneumoniae (7.5% (95% CI 4.6% to 10.4%)). However, when limited to CAP requiring hospitalisation, Staphylococcus aureus was the third most common at 4.9% (95% CI 3.9% to 5.8%). Pseudomonas aeruginosa was more frequent in hospitalised cases, while atypical pathogens were less common. Methicillin-resistant S. aureus accounted for 40.7% (95% CI 29.0% to 52.4%) of S. aureus cases. In studies that used PCR testing for pan-respiratory viral pathogens, human enterovirus/human rhinovirus (9.4% (95% CI 0% to 20.5%)) and several other respiratory pathogenic viruses were detected. The epidemiology varied depending on the methodology and situation.

CONCLUSION

The epidemiology of CAP varies depending on the situation, such as in the hospital versus outpatient setting. Viruses are more frequently detected by exhaustive genetic searches, resulting in a significant variation in epidemiology.

Atypical pneumonia: Pathophysiology, diagnosis, and treatment

Atypical pneumonia is caused by atypical pathogens that are not detectable with Gram stain and cannot be cultured using standard methods. The most common causative organisms of atypical pneumonia are Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species. The therapeutic approach for atypical pneumonias is different than that for typical pneumonia. Typical bacterial pathogens classically respond to β-lactam antimicrobial therapy because they have a cell wall amenable to β-lactam disruption. On the contrary, most atypical pathogens do not have a bacterial cell wall, some are intracellular (e.g., Legionella), and some are paracellular (e.g., M. pneumoniae). To prevent an increase in the number of antimicrobial-resistant strains, the Japanese pneumonia guidelines have proposed a differential diagnosis for typical bacterial pneumonia and atypical pneumonia to select an appropriate antibiotic for the management of mild-to-moderate pneumonia. The guidelines have set up six parameters and criteria based on the clinical symptoms, physical signs, and laboratory data. However, in the elderly individuals and patients with underlying diseases, the differential diagnosis may be difficult or a mixed infection may be latent. Therefore, in these individuals, the administration of a β-lactam drug plus a macrolide or tetracycline, or only fluoroquinolone should be considered from the beginning to cover bacterial and atypical pneumonia.

Early readmission and mortality in acute exacerbation of chronic obstructive pulmonary disease with community-acquired pneumonia

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are important causes of hospital admission and mortality. Pneumonia is a major contributor to hospitalization for AECOPD and has a close relationship with poor outcomes. We performed a prospective cohort study to evaluate the prognosis of AECOPD patients with or without community-acquired pneumonia (CAP) who hospitalized from January 2012 to December 2015. We investigated mortality and readmission rates within 6 months after the first admission between two groups and analyzed the difference of survival rate according to readmission duration (≤30 vs. >30 days) or intensive care unit (ICU) treatment. Total 308 AECOPD patients (134 with CAP and 174 without CAP) were enrolled. The mean age was 72.3 ± 9.5 years old, and 235 patients (76.3%) were male. The 180-day mortality was higher in AECOPD with CAP than without CAP (24.6% vs. 13.2%; hazard ratio (HR): 1.982; 95% CI: 1.164–3.375; p = 0.012). However, readmission rate showed no significant difference between two groups (51.5% vs. 46.6%; HR: 1.172; 95% CI: 0.850–1.616; p = 0.333). It showed a significantly lower survival rate in AECOPD with CAP rather than without CAP when were readmitted within 30 days (HR: 1.738; 95% CI:1.063–3.017; p = 0.031). According to ICU treatment, survival rate was not significantly different between two groups. Multivariate analysis revealed the readmission within 30 days (p  <  0.001), serum hemoglobin concentration (p  =  0.010), and albumin level (p =  0.049) were significantly associated with 180-day mortality of AECOPD with CAP. AECOPD with CAP showed lower survival rate than AECOPD without CAP during 6 months. Early readmission within 30 days was significantly associated with an increased risk of mortality.

Antibody responses of Chlamydophila pneumoniae pneumonia: Why is the diagnosis of C. pneumoniae pneumonia difficult?

The ELNAS Plate Chlamydophila pneumoniae commercial test kit for the detection of anti-C. pneumoniae-specific immunoglobulin M (IgM), IgA and IgG antibodies has become available in Japan recently. To determine the optimum serum collection point for the ELNAS plate in the diagnosis of C. pneumoniae pneumonia, we analyzed the kinetics of the antibody response in patients with laboratory-confirmed C. pneumoniae pneumonia. We enrolled five C. pneumoniae pneumonia cases and collected sera from patients for several months. The kinetics of the IgM and IgG antibody responses were similar among the five patients. Significant increases in IgM and IgG antibody titer between paired sera were observed in all patients. IgM antibodies appeared approximately 2-3 weeks after the onset of illness, reached a peak after 4-5 weeks, and were generally undetectable after 3-5 months. IgG antibodies developed slowly for the first 30 days and reached a plateau approximately 3-4 months after the onset of illness. The kinetics of IgA antibody responses were different among the five patients, and significant increases in IgA antibody titer between paired sera were observed in only two patients. Although the sample size was small, the best serum collection time seemed to be approximately 3-6 weeks after onset of illness when using a single serum sample for the detection of IgM antibodies. Paired sera samples should be obtained at least 4 weeks apart. IgA antibody analysis using ELNAS may not be a useful marker for acute C. pneumoniae pneumonia.

Clinical and microbiological features of patients admitted to the intensive care unit with nursing and healthcare-associated pneumonia

OBJECTIVE

To evaluate clinical and microbiological features in patients with nursing and healthcare-associated pneumonia (NHCAP), admitted to the intensive care unit (ICU).

METHODS

Demographic, clinical and microbiological data were retrospectively reviewed from patients with NHCAP admitted to a respiratory ICU. Patients were categorized into one of four NHCAP groups: (A) residence in a long-term nursing-home setting or healthcare home; (B) hospital discharge in the preceding 90 days; (C) elderly or physically disabled patients who stay at home but require healthcare; (D) continuously receiving outpatient endovascular therapy including chronic dialysis, anticancer drugs, and immunosuppressants. Pneumonia severity index (PSI), CURB-65, duration of ICU stay and 30-day mortality were evaluated.

RESULTS

Out of 428 patients reviewed (male, 67.1%; mean age, 71.2 ± 11.9 years), 30-day mortality was 25.5%, and duration of ICU stay was 13.8 ± 13.3 days. Mortality rate was not significantly different between the four NHCAP groups; duration of ICU stay was significantly longer in groups C and D. PSI score, serum HCO3(-) level, duration of ICU stay, extended spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae and multidrug resistant (MDR) Acinetobacter baumannii were significantly associated with 30-day mortality.

CONCLUSION

ESBL-producing K. pneumoniae, MDR A. baumannii and PSI score should be considered in ICU patients with NHCAP.

Risk factors for drug-resistant pathogens in community-acquired and healthcare-associated pneumonia

RATIONALE

Identification of patients with drug-resistant pathogens at initial diagnosis is essential for treatment of pneumonia.

OBJECTIVES

To elucidate clinical features of community-acquired pneumonia (CAP) and healthcare-associated pneumonia (HCAP), and to clarify risk factors for drug-resistant pathogens in patients with CAP and HCAP.

METHODS

A prospective observational study was conducted in hospitalized patients with pneumonia at 10 institutions in Japan. Pathogens identified as not susceptible to ceftriaxone, ampicillin-sulbactam, macrolides, and respiratory fluoroquinolones were defined as CAP drug-resistant pathogens (CAP-DRPs).

MEASUREMENTS AND MAIN RESULTS

In total, 1,413 patients (887 CAP and 526 HCAP) were analyzed. CAP-DRPs were more frequently found in patients with HCAP (26.6%) than in patients with CAP (8.6%). Independent risk factors for CAP-DRPs were almost identical in patients with CAP and HCAP. These included prior hospitalization (adjusted odds ratio [AOR], 2.06; 95% confidence interval [CI], 1.23-3.43), immunosuppression (AOR, 2.31; 95% CI, 1.05-5.11), previous antibiotic use (AOR, 2.45; 95% CI, 1.51-3.98), use of gastric acid-suppressive agents (AOR, 2.22; 95% CI, 1.39-3.57), tube feeding (AOR, 2.43; 95% CI, 1.18-5.00), and nonambulatory status (AOR, 2.45; 95% CI, 1.40-4.30) in the combined patients with CAP and HCAP. The area under the receiver operating characteristic curve for counting the number of risk factors was 0.79 (95% CI, 0.74-0.84).

CONCLUSIONS

The clinical profile of HCAP was different from that of CAP. However, physicians can predict drug resistance in patients with either CAP or HCAP by taking account of the cumulative number of the risk factors. Clinical trial registered with https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr.cgi?function=brows&action=brows&type=summary&recptno=R000004001&language=E ; number UMIN000003306.

Diagnostic features of community-acquired pneumonia in children: what's new?

AIM

To critically summarise the available data on diagnosis of CAP in children, focusing on the newest findings and on the need for new studies.

METHODS

Eighty studies on the diagnosis of paediatric community-acquired pneumonia were scrutinised.

RESULTS

We found no significant associations between the signs or symptoms and aetiology of pneumonia and concluded that chest radiographs remain controversial and real-time polymerase chain reaction appears more sensitive than blood cultures.

CONCLUSION

Antibiotic overuse could make it difficult to differentiate viral and bacterial causes. Molecular methods provide promising tools for diagnosing infection by atypical bacteria, but are expensive and should be used selectively.

Chlamydophila pneumoniae serology: cross-reaction with Mycoplasma pneumoniae infection

Atypical pathogens Mycoplasma pneumoniae and Chlamydophila pneumoniae play an important role in community-acquired pneumonia. However, it has been pointed out that positive enzyme-linked immunosorbent assay (ELISA, Hitazyme C. pneumoniae) IgM reactivity is frequent among M. pneumoniae pneumonia patients. To clarify the reactivity of ELISA IgM in M. pneumoniae pneumonia, findings were compared with immunoblotting, ELNAS Plate C. pneumoniae (ELNAS) and the micro-immunofluorescence (MIF) test. Ninety-eight serologically confirmed cases with M. pneumoniae pneumonia and 10 cases with C. pneumoniae pneumonia were enrolled in this study. C. pneumoniae IgM-positive cases measured by the ELISA were observed in 30 (30 %) patients with M. pneumoniae pneumonia. However, there were no positive cases by immunoblotting, ELNAS, or MIF test. These cases determined to be IgM positive only in the ELISA were all negative by another serological test, recombinant enzyme immunoassay (rEIA), and these positive results in the ELISA were considered to be false-positive reactions. In contrast, IgM-positive findings in patients with C. pneumoniae pneumonia did not show any positive reaction in M. pneumoniae antibody titer. ELISA showed a high frequency of false-positive findings in patients with M. pneumoniae pneumonia, which included false-positive cases with a high titer for IgM. To accurately diagnose C. pneumoniae infection in various studies, including respiratory infections, researchers should consider the IgM false-positive reaction with ELISA in patients with suspected atypical pneumonia.

Comparative Seroepidemiologic Analysis of Chlamydophila Pneumoniae Infection using Microimmunofluorescence, Enzyme Immunoassay and Neutralization Test: Implications for Serodiagnosis

A seroepidemiologic study using the microimmunofluorescence (MIF) technique was conducted to determine the prevalence of Chlamydophila pneumoniae IgG antibodies among 205 healthy Singapore university undergraduates using the MRL Diagnostics MIF test kit. The overall seroprevalence was 35.1% with significantly higher seropositivity rates among males than females (48.2 vs. 18.7%, P < 0.001). A comparative study using the Labsystems MIF test kit was conducted on sera from 192 students. Using the MRL MIF test as the reference, the sensitivity and specificity of Labsystems MIF test were 92.6 and 87.9%, respectively. A total of 78 samples comprising 15 MIF-negative and 63 MIF-positive samples were also tested for complement-independent neutralizing antibodies in vitro. All the 78 samples and 11 additional MIF-negative samples were also tested for IgM, IgG and IgA against C. pneumoniae by enzyme immunoassay (EIA) using the Labsystems EIA test kit. None of these 89 samples were seropositive for IgM. The percentages of IgG and IgA seropositivity increased with increasing grades of MIF-positivity. Among the IgG seropositive samples, 69.1% were also positive for IgA, suggesting that a high proportion of infected individuals also had IgA antibodies denoting chronicity. Neutralizing antibodies were detected in 22.2% of MIF-positive sera, but only in 6.7% of MIF-negative sera. 26.4 and 34.2% of samples which were IgG and IgA seropositive respectively also exhibited neutralizing activity. The percentages of MIF-positive sera with neutralizing activity increased with the grade of MIF positivity, i.e. 0% (1+), 7.1% (2+), 18.8% (3+), and 63.6% (4+). High-grade MIF positivity (particularly with MRL MIF kits) may represent a useful serologic marker of predictive value for neutralizing activity.

Genomic screening for Chlamydophila pneumoniae-specific antigens using serum samples from patients with primary infection

Chlamydophila pneumoniae, an obligate intracellular human pathogen, causes respiratory tract infections. The most common techniques used for the serological diagnosis of C. pneumoniae infections are microimmunofluorescence tests and commercial serological ELISA tests; these are based on the detection of antibodies against whole chlamydial elementary bodies and lipopolysaccharide/outer membrane protein, respectively. Identification of more specific and highly immunodominant antigens is essential for the development of new serodiagnostic assays. To identify novel specific antigens from C. pneumoniae, we screened 455 genes with unknown function in the genome of C. pneumoniae J138. Extracts of Saccharomyces cerevisiae cells expressing GFP-tagged C. pneumoniae proteins were subjected to Western blot analysis using serum samples from C. pneumoniae-infected patients as the primary antibodies. From this comprehensive analysis, 58 clones expressing C. pneumoniae open reading frames, including hypothetical proteins, were identified as antigens. These results have provided useful information for the development of new serological tools for the diagnosis for C. pneumoniae infections and for the development of vaccines in future.

The validity of the criteria for primary infection of Chlamydophila pneumoniae in children by measuring ELISA IgM antibodies

As IgM antibody measurement by enzyme-linked immunosorbent assay (ELISA) has become possible for the serological diagnosis of Chlamydophila pneumoniae (C. pn) infection, the HITAZYME-ELISA method has become widely employed in Japan. However, in children, when the diagnostic criterion of primary infection is set at ID ≥1.1, the positive rate is higher than expected, and the potential for inaccurate reflection of the prevalence has been raised. In this study, we performed ROC analysis involving 136 pediatric patients with acute airway symptoms (0-14 years of age), considering a 32-fold or higher micro-immunofluorescence IgM antibody titer against C. pn as positive. Setting the cut-off value for ELISA C. pn IgM antibody ID at 2.0, the specificity was 100%, with no false positivity. The maximum (sensitivity + specificity)/2 was obtained when the cut-off value was set at 1.5. Therefore, IgM ID ≥2.0 was regarded as definitely positive and an IgM ID between 1.5 and 2.0 was regarded as indeterminate as diagnostic criteria for the primary infection. When the prevalence was investigated in 3,108 children (0-15 years of age) with airway symptoms based on these criteria, 542 cases (17.4%) were positive, and the median duration of IgM antibody positivity was five months. Long-term positivity (ten cases) for more than 12 months and recurrent positivity (eight cases) were also observed, but it may be appropriate to set a new criterion of IgM antibody ID ≥2.0 for the diagnosis of primary Chlamydophila pneumoniae infection in children.