Transmission of Severe Fever with Thrombocytopenia Syndrome Virus to Human from Nonindigenous Tick Host, Japan.

We report a human case of severe fever with thrombocytopenia syndrome virus infection transmitted by a tick, confirmed by viral identification. Haemaphysalis aborensis, a tick species not native to Japan that has been observed to transmit the virus to humans, is now recognized as a potential vector of this virus in Japan.

Post-Transcriptional Induction of the Antiviral Host Factor GILT/IFI30 by Interferon Gamma.

Gamma-interferon-inducible lysosomal thiol reductase (GILT) plays pivotal roles in both adaptive and innate immunities. GILT exhibits constitutive expression within antigen-presenting cells, whereas in other cell types, its expression is induced by interferon gamma (IFN-γ). Gaining insights into the precise molecular mechanism governing the induction of GILT protein by IFN-γ is of paramount importance for adaptive and innate immunities. In this study, we found that the 5' segment of GILT mRNA inhibited GILT protein expression regardless of the presence of IFN-γ. Conversely, the 3' segment of GILT mRNA suppressed GILT protein expression in the absence of IFN-γ, but it loses this inhibitory effect in its presence. Although the mTOR inhibitor rapamycin suppressed the induction of GILT protein expression by IFN-γ, the expression from luciferase sequence containing the 3' segment of GILT mRNA was resistant to rapamycin in the presence of IFN-γ, but not in its absence. Collectively, this study elucidates the mechanism behind GILT induction by IFN-γ: in the absence of IFN-γ, GILT mRNA is constitutively transcribed, but the translation process is hindered by both the 5' and 3' segments. Upon exposure to IFN-γ, a translation inhibitor bound to the 3' segment is liberated, and a translation activator interacts with the 3' segment to trigger the initiation of GILT translation.

Coronavirus Disease 19 (COVID-19) Vaccine Effectiveness Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection During Delta-Dominant and Omicron-Dominant Periods in Japan: A Multicenter Prospective Case-control Study (Factors Associated with SARS-CoV-2 Infection and the Effectiveness of COVID-19 Vaccines Study).

BACKGROUND: Although several coronavirus disease 2019 (COVID-19) vaccines initially showed high efficacy, there have been concerns because of waning immunity and the emergence of variants with immune escape capacity. METHODS: A test-negative design case-control study was conducted in 16 healthcare facilities in Japan during the Delta-dominant period (August-September 2021) and the Omicron-dominant period (January-March 2022). Vaccine effectiveness (VE) against symptomatic severe acute respiratory syndrome coronavirus 2 infection was calculated for 2 doses for the Delta-dominant period and 2 or 3 doses for the Omicron-dominant period compared with unvaccinated individuals. RESULTS: The analysis included 5795 individuals with 2595 (44.8%) cases. Among vaccinees, 2242 (55.8%) received BNT162b2 and 1624 (40.4%) received messenger RNA (mRNA)-1273 at manufacturer-recommended intervals. During the Delta-dominant period, VE was 88% (95% confidence interval [CI], 82-93) 14 days to 3 months after dose 2 and 87% (95% CI, 38-97) 3 to 6 months after dose 2. During the Omicron-dominant period, VE was 56% (95% CI, 37-70) 14 days to 3 months since dose 2, 52% (95% CI, 40-62) 3 to 6 months after dose 2, 49% (95% CI, 34-61) 6+ months after dose 2, and 74% (95% CI, 62-83) 14+ days after dose 3. Restricting to individuals at high risk of severe COVID-19 and additional adjustment for preventive measures (ie, mask wearing/high-risk behaviors) yielded similar estimates, respectively. CONCLUSIONS: In Japan, where most are infection-naïve, and strict prevention measures are maintained regardless of vaccination status, 2-dose mRNA vaccines provided high protection against symptomatic infection during the Delta-dominant period and moderate protection during the Omicron-dominant period. Among individuals who received an mRNA booster dose, VE recovered to a high level.

Social and Behavioral Factors Associated with Lack of Intent to Receive COVID-19 Vaccine, Japan.

Persons in Japan who did not intend to receive COVID-19 vaccines after widespread rollout were less likely than others to engage in preventive measures or to be afraid of getting infected or infecting others. They were also not less likely to engage in potentially high-risk behaviors, suggesting similar or higher exposure risks.

High prevalence of multiple serotypes of pneumococci in patients with pneumonia and their associated risk factors.

BACKGROUND: Multiple serotypes of pneumococci have epidemiological and clinical implications, such as the emergence of non-vaccine serotypes and the acquisition of antimicrobial resistance. Prevalence of multiple serotypes of pneumococci in adults and their risk factors are not known. METHODS: We enrolled adult patients from age ≥15 years with radiologically confirmed pneumonia in four hospitals across Japan. Pneumococcal pneumonia was defined with a pneumococcal bacterial density of ≥104/mL in sputum by lytA quantitative PCR, and serotypes were determined. Pneumonias with a single serotype were categorised as single-serotype pneumococcal pneumonia and with two or more serotypes as multiple-serotype pneumococcal pneumonia. Multivariable logistic regression was used to assess the risk factors. RESULTS: 3470 patients (median age 77 years, IQR 65-85) were enrolled. Pneumococcal pneumonia was identified in 476 (18.3%, n=2605) patients. Multiple serotypes were detected in 42% of them. Risk of having multiple serotypes was low among patients who had received 23-valent pneumococcal polysaccharide vaccine (PPSV23) vaccines (adjusted OR 0.51 (95% CI 0.27 to 0.94)). Proportion of non-PCV7 PPSV23 serotypes in overall distribution of multiple serotypes was 67.4% (n=324/481) compared with 46.4% (n=128/276) in that of single serotypes (p=0.001). Serotypes 5, 9N/9L, 10A, 12/22/46, 17F and 35F were associated with multiple-serotype pneumonia, and serotypes 6A/6B, 23F, 11 and 6C/6D were associated with single-serotype pneumonia. Proportion of more invasive serotypes (serotypes 1, 5, 7F, 8) was significantly higher in multiple-serotype pneumonia (p=0.001). CONCLUSIONS: Multiple serotypes of pneumococci are common in sputum of adult patients with pneumonia. The risk of multiple-serotype pneumococcal pneumonia is lower than that of single-serotype pneumococcal pneumonia among PPSV23-vaccinated patients. TRIAL REGISTRATION NUMBER: UMIN000006909.

Clinical and microbiological characteristics and challenges in diagnosing infected aneurysm: a retrospective observational study from a single center in Japan.

BACKGROUND: It is challenging to diagnose infected aneurysm in the early phase. This study aimed to describe the clinical and microbiological characteristics of infected aneurysm, and to elucidate the difficulties in diagnosing the disease. METHODS: Forty-one cases of infected aneurysm were diagnosed in Nagasaki University Hospital from 2005 to 2019. Information on clinical and microbiological characteristics, radiological findings, duration of onset, and type of initial computed tomography (CT) imaging conditions were collected. Factors related to diagnostic delay were analyzed by Fisher's exact test for categorical variables or by the Wilcoxon rank-sum test for continuous variables. RESULTS: Pathogens were identified in 34 of 41 cases; the pathogens were Gram-positive cocci in 16 cases, Gram-negative rods in 13 cases, and others in five cases. Clinical characteristics did not differ in accordance with the identified bacteria. At the time of admission, 16 patients were given different initial diagnoses, of which acute pyelonephritis (n = 5) was the most frequent. Compared with the 22 patients with an accurate initial diagnosis, the 19 initially misdiagnosed patients were more likely to have been examined by plain CT. The sensitivities of plain CT and contrast-enhanced CT were 38.1% and 80.0%, respectively. CONCLUSIONS: In cases of infected aneurysm, diagnostic delay is attributed to non-specific symptoms and the low sensitivity of plain CT. Clinical characteristics of infected aneurysm mimic various diseases. Contrast-enhanced CT should be considered if infected aneurysm is suspected.

Diphtheria in Metro Manila, the Philippines 2006-2017: A Clinical, Molecular, and Spatial Characterization.

BACKGROUND: Diphtheria is a vaccine-preventable disease that persists as a global health problem. An understanding of the pattern of disease is lacking in low- and middle-income countries such as the Philippines. METHODS: We conducted a retrospective review of the clinical, microbiological, and epidemiological features of patients admitted with a clinical diagnosis of diphtheria to an infectious disease referral hospital in Metro Manila, the Philippines, between 2006 and 2017. Cases were mapped and the distribution was compared with population density. Corynebacterium diphtheriae isolates from between 2015 and 2017 were examined by multilocus sequence typing (MLST). RESULTS: We studied 267 patients (range:12-54 cases/year) admitted between 2006 and 2017. The case fatality rate (CFR) was 43.8% (95% confidence interval, 37.8-50.0%). A higher number of cases and CFR was observed among children <10 years. Mortality was associated with a delayed admission to hospital and a lack of diphtheria antitoxin. Between 2015 and 2017 there were 42 laboratory-confirmed cases. We identified 6 multilocus sequence types (STs). ST-302 was the most common (17/34, 48.6%), followed by ST67 (7/34, 20%) and ST458 (5/34, 14%). Case mapping showed a wide distribution of diphtheria patients in Metro Manila. Higher case numbers were found in densely populated areas but with no apparent clustering of ST types. CONCLUSIONS: Our analysis indicates that diphtheria remains endemic in Metro Manila and that the infection is frequently fatal in young children. Improved vaccine coverage and a sustainable supply of diphtheria antitoxin should be prioritized.

Progress towards antibiotic use targets in eight high-income countries.

OBJECTIVE: To compare antibiotic sales in eight high-income countries using the 2019 World Health Organization (WHO) Access, Watch and Reserve (AWaRe) classification and the target of 60% consumption of Access category antibiotics. METHODS: We analysed data from a commercial database of sales of systemic antibiotics in France, Germany, Italy, Japan, Spain, Switzerland, United Kingdom of Great Britain and Northern Ireland, and United States of America over the years 2013-2018. We classified antibiotics according to the 2019 AWaRe categories: Access, Watch, Reserve and Not Recommended. We measured antibiotic sales per capita in standard units (SU) per capita and calculated Access group sales as a percentage of total antibiotic sales. FINDINGS: In 2018, per capita antibiotic sales ranged from 7.4 SU (Switzerland) to 20.0 SU (France); median sales of Access group antibiotics were 10.9 SU per capita (range: 3.5-15.0). Per capita sales declined moderately over 2013-2018. The median percentage of Access group antibiotics was 68% (range: 22-77 %); the Access group proportion increased in most countries between 2013 and 2018. Five countries exceeded the 60% target; two countries narrowly missed it (> 55% in Germany and Italy). Sales of Access antibiotics in Japan were low (22%), driven by relatively high sales of oral cephalosporins and macrolides. CONCLUSION: We have identified changes to prescribing that could allow countries to achieve the WHO target. The 60% Access group target provides a framework to inform national antibiotic policies and could be complemented by absolute measures and more ambitious values in specific settings.

Pneumatocele formation in a fatal adult pneumonia patient coinfected with Streptococcus pyogenes emm-type 3 and influenza A: a case report.

BACKGROUND: A pneumatocele is a transient thin-walled lesion and rare complication in adult pneumonia. A variety of infectious pathogens have been reported in children with pneumatoceles. We report the first case of adult pneumonia with pneumatocele formation that is likely caused by Streptococcus pyogenes and coinfection with influenza A virus. CASE PRESENTATION: A 64-year-old Japanese man presented with a one-week history of fever, sore throat, and arthralgia. He was referred to our university hospital for respiratory distress. He required mechanical ventilation in the intensive care unit (ICU). Bacterial culture detected S. pyogenes in the bronchoscopic aspirates, which was not detected in blood. Although a rapid influenza antigen test was negative, an influenza A polymerase chain reaction (PCR) test was positive. Therefore, he was diagnosed with coinfection of influenza A and group A streptococcus (GAS) pneumonia complicated by probable streptococcal toxic shock syndrome. A chest radiograph on admission showed diffuse patchy opacification and consolidation in the bilateral lung fields. Multiple thin-walled cysts appeared in both middle lung fields on computed tomography (CT). On the following day, the bilateral cysts had turned into a mass-like opacity. The patient died despite intensive care. An autopsy was performed. The pathology investigation revealed multiple hematomas formed by bleeding in pneumatoceles. CONCLUSIONS: There have been no previous reports of a pneumatocele complicated by S. pyogenes in an adult patient coinfected with influenza A. Further molecular investigation revealed that the S. pyogenes isolate had the sequence type of emm3.

Rickettsia japonica Infection after Land Leech Bite, Japan.

We report a case of Rickettsia japonica infection in an 81-year-old man in central Japan. The patient had fever, rash, and an eschar but no evidence of a tick bite. His symptoms began 8 days after a land leech bite. The land leech is a potential vector of R. japonica.

An alarmingly high nasal carriage rate of Streptococcus pneumoniae serotype 19F non-susceptible to multiple beta-lactam antimicrobials among Vietnamese children.

BACKGROUND: Understanding the relationship between serotype epidemiology and antimicrobial susceptibility of Streptococcus pneumoniae is essential for the effective introduction of pneumococcal conjugate vaccines (PCVs) and control of antimicrobial-resistant pneumococci. METHODS: We conducted a community-based study in Nha Trang, central Vietnam, to clarify the serotype distribution and pattern of S. pneumoniae antimicrobial susceptibility in children under 5 years of age and to identify risk factors for carrying antimicrobial-resistant strains. Nasopharyngeal swabs collected from children with acute respiratory infections (ARIs) hospitalized between April 7, 2008, and March 30, 2009, and from healthy children randomly selected in July 2008 were subjected to bacterial culture. Minimum inhibitory concentrations (MICs) against S. pneumoniae were determined, and multiplex-polymerase chain reaction (PCR) serotyping assays were performed. Logistic regression was applied to identify risk factors. RESULTS: We collected 883 samples from 331 healthy children and 552 ARI cases; S. pneumoniae was isolated from 95 (28.7%) healthy children and 202 (36.6%) ARI cases. Age and daycare attendance were significantly associated with pneumococcal carriage. In total, 18.0, 25.8 and 75.6% of the isolates had high MICs for penicillin (≥4 µg/ml), cefotaxime (≥2 µg/ml) and meropenem (≥0.5 µg/ml), respectively. The presence of pneumococci non-susceptible to multiple beta-lactams was significantly associated with serotype 19F (Odds Ratio: 4.23) and daycare attendance (Odds Ratio: 2.56) but not ARIs, age or prior antimicrobial use. The majority of isolates non-susceptible to multiple beta-lactams (90%) were PCV13 vaccine serotypes. CONCLUSIONS: S. pneumoniae serotype 19F isolates non-susceptible to multiple beta-lactams are widely prevalent among Vietnamese children. Vaccine introduction is expected to significantly increase drug susceptibility.

Dose-Dependent Negative Effects of Prior Multiple Vaccinations Against Influenza A and Influenza B Among Schoolchildren: A Study of Kamigoto Island in Japan During the 2011-2012, 2012-2013, and 2013-2014 Influenza Seasons.

Background: We investigated the negative effects of prior multiple vaccinations on influenza vaccine effectiveness (VE) and analyzed the association of VE with prior vaccine doses. Methods: Patients aged 9-18 years presenting with influenza-like illness at a community hospital on a remote Japanese island during the 2011-2012, 2012-2013, and 2013-2014 influenza seasons were tested for influenza using a rapid diagnostic test (RDT). A test-negative, case-control study design was used to estimate the VEs of trivalent inactivated influenza vaccine. Histories of vaccination and medically attended influenza (MA-flu) A and B during 3 previous seasons were collected from registry systems. VE was calculated using multilevel mixed-effects logistic regression models adjusted for the history of RDT-confirmed MA-flu. Results: During 3 influenza seasons, 1668 influenza-like illness episodes were analyzed, including 421 and 358 episodes of MA-fluA and MA-fluB, respectively. The adjusted VE (95% confidence interval) yielded significant dose-dependent attenuations by prior vaccinations against both MA-fluA (0 doses during previous 3 seasons: 96% [69%-100%], 1 dose: 48% [-7% to 74%], 2 doses: 52% [11%-74%], 3 doses: 21% [-25% to 51%]; P for trend < .05) and MA-fluB (0 doses: 66% [-5% to 89%], 1 dose: 48% [-14% to 76%], 2 doses: 34% [-33% to 67%], 3 doses: -7% [-83% to 37%]; P for trend < .05). After excluding episodes of MA-flu during prior 3 seasons, similar trends were observed. Conclusions: Repeated previous vaccinations over multiple seasons had significant dose-dependent negative impacts on VE against both MA-fluA and MA-fluB. Further studies to confirm this finding are necessary.

Distinguishing Japanese Spotted Fever and Scrub Typhus, Central Japan, 2004- 2015.

Japanese spotted fever (JSF) and scrub typhus (ST) are endemic to Japan and share similar clinical features. To document the clinical and epidemiologic characteristics that distinguish these 2 rickettsial diseases, during 2004-2015 we recruited 31 JSF patients, 188 ST patients, and 97 nonrickettsial disease patients from the southern Boso Peninsula of Japan. JSF occurred during April-October and ST during November-December. Patients with JSF and ST were significantly older and more likely to reside in wooded areas than were patients with nonrickettsial diseases. Spatial analyses revealed that JSF and ST clusters rarely overlapped. Clinical findings more frequently observed in JSF than in ST patients were purpura, palmar/plantar rash, hyponatremia, organ damage, and delayed defervescence after treatment. Although their clinical features are similar, JSF and ST differ in seasonality, geographic distribution, physical signs, and severity. Because a considerable percentage of patients did not notice rash and eschar, many rickettsial diseases might be underdiagnosed in Japan.

Severe Pneumonia Caused by Toxigenic Corynebacterium ulcerans Infection, Japan.

Corynebacterium ulcerans infection was recently recognized as a zoonosis. We present 2 cases of severe pneumonia complicated by diffuse pseudomembrane formation on the bronchus caused by C. ulcerans-producing diphtheria toxin. Our purpose is to alert medical professionals to the virulence of Corynebacterium species other than C. diphtheriae.

Accuracy of High-Throughput Nanofluidic PCR-Based Pneumococcal Serotyping and Quantification Assays Using Sputum Samples for Diagnosing Vaccine Serotype Pneumococcal Pneumonia: Analyses by Composite Diagnostic Standards and Bayesian Latent Class Models.

The lack of reliable diagnostic tests for detecting vaccine serotype pneumococcal pneumonia (VTPP) remains a challenging issue in pneumococcal vaccine studies. This study assessed the performances of high-throughput nanofluidic PCR-based pneumococcal serotyping and quantification assay methods using sputum samples (the nanofluidic sputum quantitative PCR [Sp-qPCR] assay) to diagnose 13-valent pneumococcal conjugate VTPP compared with the performance of the serotype-specific urinary antigen detection (UAD) assay using urine samples. Adult pneumonia patients from Japan were enrolled in this study between September 2012 and August 2014. Sputum samples were subjected to the nanofluidic Sp-qPCR assay, quantitatively cultured, and serotyped by the Quellung reaction (SpQt). Urine samples were tested by the UAD method. The diagnostic performances of these tests were assessed using composite reference standards and Bayesian latent class models (BLCMs). Among 244 total patients, 27 (11.1%) tested positive with the UAD assay, while 16 (6.6%) and 34 (13.9%) tested positive with the SpQt and nanofluidic Sp-qPCR assays, respectively, with a cutoff value of ≥104 DNA copies/ml, which showed the maximum value of the Youden index. Using BLCMs, the estimated prevalence for VTPP was 12.9%, and the nanofluidic Sp-qPCR assay demonstrated the best performance (sensitivity, 90.2%; specificity, 96.9%), followed by UAD (sensitivity, 75.6%; specificity, 97.9%) and SpQt (sensitivity, 45.8%; specificity, 99.5%). However, when a higher cutoff value of ≥107 DNA copies/ml was applied, the performance of UAD became comparable to that of Sp-qPCR. The vaccine serotype-specific pneumococcal DNA load in sputum among UAD-positive patients was 3 logs higher than that among UAD-negative patients (P = 0.036). The nanofluidic Sp-qPCR assay may be accurate and useful for detecting VTPP among adults.

Six underlying health conditions strongly influence mortality based on pneumonia severity in an ageing population of Japan: a prospective cohort study.

BACKGROUND: Mortality prediction of pneumonia by severity scores in patients with multiple underlying health conditions has not fully been investigated. This prospective cohort study is to identify mortality-associated underlying health conditions and to analyse their influence on severity-based pneumonia mortality prediction. METHODS: Adult patients with community-acquired pneumonia or healthcare-associated pneumonia (HCAP) who visited four community hospitals between September 2011 and January 2013 were enrolled. Candidate underlying health conditions, including demographic and clinical characteristics, were incorporated into the logistic regression models, along with CURB (confusion, elevated urea nitrogen, tachypnoea, and hypotension) score as a measure of disease severity. The areas under the receiver operating characteristic curves (AUROC) of the predictive index based on significant underlying health conditions was compared to that of CURB65 (CURB and age ≥ 65) score or Pneumonia severity index (PSI). Mortality association between disease severity and the number of underlying health conditions was analysed. RESULTS: In total 1772 patients were eligible for analysis, of which 140 (7.9%) died within 30 days. Six underlying health conditions were independently associated: home care (adjusted odds ratio, 5.84; 95% confidence interval, CI, 2.28-14.99), recent hospitalization (2.21; 1.36-3.60), age ≥ 85 years (2.15; 1.08-4.28), low body mass index (1.99, 1.25-3.16), neoplastic disease (1.82; 1.17-2.85), and male gender (1.78; 1.16-2.75). The predictive index based on these conditions alone had a significantly or marginally higher AUROC than that based on CURB65 score (0.78 vs 0.66, p = 0.02) or PSI (0.78 vs 0.71, p = 0.05), respectively. Compared to this index, the AUROC of the total score consisting of six underlying health conditions and CURB score (range 0-10) did not improve mortality predictions (p = 0.3). In patients with one or less underlying health conditions, the mortality was discretely associated with severe pneumonia (CURB65 ≥ 3) (risk ratio: 7.24, 95%CI: 3.08-25.13), whereas in patients with 2 or more underlying health conditions, the mortality association with severe pneumonia was not detected (risk ratio: 1.53, 95% CI: 0.94-2.50). CONCLUSIONS: Mortality prediction based on pneumonia severity scores is highly influenced by the accumulating number of underlying health conditions in an ageing society. The validation using a different cohort is necessary to generalise the conclusion.

Risk for Death among Children with Pneumonia, Afghanistan.

In Afghanistan, childhood deaths from pneumonia are high. Among 639 children at 1 hospital, the case-fatality rate was 12.1%, and 46.8% of pneumococcal serotypes detected were covered by the 13-valent vaccine. Most deaths occurred within 2 days of hospitalization; newborns and malnourished children were at risk. Vaccination could reduce pneumonia and deaths.

The impact of virus infections on pneumonia mortality is complex in adults: a prospective multicentre observational study.

BACKGROUND: Various viruses are known to be associated with pneumonia. However, the impact of viral infections on adult pneumonia mortality remains unclear. This study aimed to clarify the effect of virus infection on pneumonia mortality among adults stratified by virus type and patient comorbidities. METHODS: This multicentre prospective study enrolled pneumonia patients aged ≥15 years from September 2011 to August 2014. Sputum samples were tested by in-house multiplex polymerase chain reaction assays to identify 13 respiratory viruses. Viral infection status and its effect on in-hospital mortality were examined by age group and comorbidity status. RESULTS: A total of 2617 patients were enrolled in the study and 77.8% was aged ≥65 years. 574 (21.9%) did not have comorbidities, 790 (30.2%) had chronic respiratory disease, and 1253 (47.9%) had other comorbidities. Viruses were detected in 605 (23.1%) patients. Human rhinovirus (9.8%) was the most frequently identified virus, followed by influenza A (3.9%) and respiratory syncytial virus (3.9%). Respiratory syncytial virus was more frequently identified in patients with chronic respiratory disease (4.7%) than those with other comorbidities (4.2%) and without comorbidities (2.1%) (p = 0.037). The frequencies of other viruses were almost identical between the three groups. Virus detection overall was not associated with increased mortality (adjusted risk ratio (ARR) 0.76, 95% CI 0.53-1.09). However, influenza virus A and B were associated with three-fold higher mortality in patients with chronic respiratory disease but not with other comorbidities (ARR 3.38, 95% CI 1.54-7.42). Intriguingly, paramyxoviruses were associated with dramatically lower mortality in patients with other comorbidities (ARR 0.10, 95% CI 0.01-0.70) but not with chronic respiratory disease. These effects were not affected by age group. CONCLUSIONS: The impact of virus infections on pneumonia mortality varies by virus type and comorbidity status in adults.

Recurrent pneumonia among Japanese adults: disease burden and risk factors.

BACKGROUND: In Japan and other societies with rapidly aging populations, recurrent pneumonia (RP) is a major clinical problem yet only limited information exists regarding the burden of this disease. METHODS: A prospective study of adult pneumonia was conducted to investigate the incidence of RP and potential risk factors. From February 1, 2012 to January 31, 2013, patients aged ≥ 15 years who were diagnosed with pneumonia were prospectively enrolled in a representative community hospital located in central Japan. Patients were followed for one-year to evaluate the recurrence of pneumonia and characteristics associated with RP. Cox proportional hazards models were constructed to compute adjusted hazard ratios (aHR) and ascertain risk factors significantly associated with RP. RESULTS: In total, 841 patients with a median age of 73 years (range 15-101 years) were enrolled totaling 1,048 person-years of observation with a median follow-up time of 475 days. A total of 137 patients had at least one recurrent episode with an incidence rate of 13.1 per 100 person-years (95% confidence interval: 11.1-15.5). In multivariate analysis, a past history of pneumonia (aHR 1.95, 95% CI: 1.35-2.8), chronic pulmonary disease (aHR 1.86, 1.24-2.78) and inhaled corticosteroid usage (aHR 1.78, 1.12-2.84) and hypnotic/sedative medication usage (aHR 2.06, 1.28-3.31) were identified as independent risk factors for recurrent pneumonia, whereas angiotensin converting enzyme-inhibitors usage was associated with a reduction of the risk of RP (aHR 0.22, 0.05-0.91). The detection of P. aeruginosa was significantly associated with RP even after adjusting for chronic pulmonary diseases (aHR = 2.37). CONCLUSIONS: Recurrent pneumonia constitutes a considerable proportion of the pneumonia burden in Japan. A past history of pneumonia, chronic pulmonary disease, inhaled corticosteroid and hypnotic/sedative medication usage and detection of P. aeruginosa were identified as independent risk factors for recurrent pneumonia and special attention regarding the use of medications in this vulnerable population is needed to reduce the impact of this disease in aging populations.