石和田 稔彦

In this study, we examined the molecular evolution of the fusion protein (F) gene in human respiratory syncytial virus subgroup B (HRSV-B). First, we performed time-scale evolution analyses using the Bayesian Markov chain Monte Carlo (MCMC) method. Next, we performed genetic distance, linear B-cell epitope prediction, N-glycosylation, positive/negative selection site, and Bayesian skyline plot analyses. We also constructed a structural model of the F protein and mapped the amino acid substitutions and the predicted B-cell epitopes. The MCMC-constructed phylogenetic tree indicated that the HRSV F gene diverged from the bovine respiratory syncytial virus gene approximately 580years ago and had a relatively low evolutionary rate (7.14×10-4substitutions/site/year). Furthermore, a common ancestor of HRSV-A and -B diverged approximately 290years ago, while HRSV-B diverged into three clusters for approximately 60years. The genetic similarity of the present strains was very high. Although a maximum of 11 amino acid substitutions were observed in the structural model of the F protein, only one strain possessed an amino acid substitution located within the palivizumab epitope. Four epitopes were predicted, although these did not correspond to the neutralization sites of the F protein including the palivizumab epitope. In addition, five N-glycosylation sites of the present HRSV-B strains were inferred. No positive selection sites were identified; however, many sites were found to be under negative selection. The effective population size of the gene has remained almost constant. On the basis of these results, it can be concluded that the HRSV-B F gene is highly conserved, as is the F protein of HRSV-A. Moreover, our prediction of B-cell epitopes does not show that the palivizumab reaction site may be recognized as an epitope during naturally occurring infections.

パリビズマブ投与目的で千葉県内の8つの医療機関を受診した小児325例を対象に、パリビズマブ単独投与群108例とパリビズマブ+ワクチン同時接種群217例に分け、有害事象や副反応について比較検討した。その結果、副反応はパリビズマブ単独投与群で3例(2.8%)、パリビズマブ+ワクチン同時接種群で3例(1.4%)に認め、両群間で有意差はみられなかった。副反応は局所発赤や腫脹などが主体であり、いずれの症状も自然に改善していた。両群ともに副反応以外の有害事象は認めなかった。

QuantiFERON-TB gold in-tube has been used for screening latent tuberculosis infection in newly employed health care workers in Japan. There have been a few studies concerning quality control. We retrospectively analysed QuantiFERON-TB gold in-tube results in a hospital in Japan. Interferon-γ values in three blood collection tubes for QuantiFERON-TB gold in-tube were analysed in association with the positivity rate. The data set consisted of health care workers aged 20-29 years during the 7 years between 2010 and 2016. The yearly QuantiFERON-TB gold in-tube positivity rate was 0.9%, 16.4%, 3.0%, 39.3%, 2.8%, 0.9% and 1.5%, and was extremely high in 2011 and 2013. The interferon-γ values in the tuberculosis antigen tube were elevated in these two years, as indicated by higher median and wider interquartile range. The interferon-γ value in the negative control tube was also higher in 2011. The higher interferon-γ values in collection tubes (tuberculosis antigen tube and/or negative control tube) resulted in higher QuantiFERON-TB gold in-tube positivity rate. The distribution of interferon-γ in tuberculosis antigen tube and negative control tube, as evaluated by median and interquartile range, proved to be an effective index for the quality control of QuantiFERON-TB gold in-tube.

Tosufloxacin (TFLX) is a fluoroquinolone antimicrobial agent. TFLX granules for children were initially released in Japan in 2010 to treat otitis media and pneumonia caused by drug-resistant bacteria, e.g. penicillin-resistant Streptococcus pneumoniae and beta-lactamase-negative, ampicillin-resistant Haemophilus influenzae. The evolution of bacterial resistance since TFLX approval is not known. To clarify the influence of quinolones administered to children since their approval, we examined the resistance mechanism of TFLX-resistant S. pneumoniae isolated from paediatric patients as well as patient clinical characteristics. TFLX-resistant strains (MIC ≥ 2 mg/L) were detected among clinical isolates of S. pneumoniae derived from children (≤15 years old) between 2010 and 2014. These strains were characterised based on quinolone resistance-determining regions (QRDRs), i.e. gyrA, gyrB, parC, and parE. In addition, the antimicrobial susceptibility, serotype, and multilocus sequence type of strains were determined, pulsed-field gel electrophoresis was performed, and patient clinical characteristics based on medical records were assessed for cases with underling TFLX-resistant strains. Among 1168 S. pneumoniae isolates, two TFLX-resistant strains were detected from respiratory specimens obtained from paediatric patients with frequent exposure to TFLX. Both strains had mutations in the QRDRs of gyrA and parC. One case exhibited gradual changes in the QRDR during the clinical course. This is the first study of quinolone-resistant S. pneumoniae isolated from children, including clinical data, in Japan. These data may help prevent increases in infections of quinolone-resistant S. pneumoniae in children; specifically, the results emphasise the importance of administering fluoroquinolones only in appropriate cases.

This study aimed to identify trends in frequency, serotype, and antimicrobial susceptibility of Streptococcus pneumoniae and Haemophilus influenzae isolated from middle ear fluid specimens of children aged≤15 years (mean, 2 years), before and after the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) and the H. influenzae type b vaccine, at a pediatric facility in Japan. Sixty-six S. pneumoniae and 88 H. influenzae strains were isolated from 820 middle ear fluid samples. Serotyping and antimicrobial susceptibility testing were performed. The study time-frame was divided into period 1 (2007-2010) and period 2 (2011-2014), according to the availability of vaccine public funding. The S. pneumoniae detection rate decreased from 9.6% in period 1-6.1% in period 2 (p = 0.042). PCV7 serotypes decreased from 56.8% to 9.1% (p = 0.0002). No significant change was observed for the 13-valent pneumococcal conjugate vaccine (PCV13) serotypes: 72.7% in period 1 and 59.1% in period 2. Penicillin-resistant strains (penicillin G-MIC ≥2 μg/mL) decreased from 25% to 4.5% (p = 0.038). Detection rates for H. influenzae did not change significantly: 10.3% in period 1 and 11.3% in period 2. Serotypes were mostly non-typeable: 97.9% in period 1 and 90.2% in period 2, and only one serotype b strain was isolated in each period. The frequency of ampicillin-resistant strains (MIC ≥4 μg/mL) did not change. These results show a preventative effect of PCV7 on otitis media due to S. pneumoniae. PCV7 was replaced with PCV13 in 2013 in Japan; therefore, a further decrease in pneumococcal otitis media is anticipated in the future.

背景・目的ノイラミニダーゼ阻害薬はA型・B型インフルエンザに対する治療薬として広く使用されている。ノイラミニダーゼ阻害薬使用後も発熱が遷延する例があり、薬剤耐性の関与も示唆されるが、B型インフルエンザにおいては詳細に解析されていない。材料と方法2013/2014シーズンにインフルエンザと診断した小児206名のうち、ノイラミニダーゼ阻害薬投与後も48時間以上発熱が遷延した10名の上咽頭ぬぐい液から検出したB型インフルエンザRNAを用い、ノイラミニダーゼの遺伝子変異部位に関して分子構造モデルを用いて解析を行った。結果B型インフルエンザはA型インフルエンザに比較し、ノイラミニダーゼ阻害薬投与後の平均有熱期間が長かった。発熱が遷延した症例から検出されたB型インフルエンザはワクチン株(B/Massachusetts/02/2012)と異なる遺伝子配列を示した。ノイラミニダーゼ阻害薬への耐性を示したM2-1 と K41-1の２検体 では、新規の変異が見出された。それらは、M2-1ではS99N, T106I, K125T, S295Rであり、K41-1ではI262M, V271T, K/E272Q, E320K, D342G, M375Kであった。分子モデルの解析の結果、特にM2-1のR295とK41-1のQ272とK375 が薬剤耐性に関与している可能性が示唆された。結論分子モデルの解析はインフルエンザウイルスに対するノイラミニダーゼ阻害薬耐性機序の解明に有用であった。耐性ウイルスの増加を抑えるために、抗インフルエンザ薬の適正使用を進めていく必要性が示唆された。

BACKGROUND: Corynebacterium striatum was recently recognized as a potential pathogen of various infectious diseases. However, the clinical entity of this microorganism has not been clearly identified. Therefore, we analyzed C. striatum isolates from blood culture and explored their clinical determinants. METHODS: We reviewed the medical records of all patients from whom C. striatum isolates were recovered from blood culture for analysis of the patients' backgrounds and clinical course including response to antimicrobial therapy and prognosis. RESULTS: During the 5-year study period (January 2010 to December 2014), 24 C. striatum strains were isolated from blood samples, and the frequency of C. striatum bacteremia increased. The majority of the strains were multidrug resistant. All of the tested strains were susceptible to only vancomycin. The age at onset of C. striatum bacteremia encompassed all adult age groups, and at least one underlying condition was documented in all patients. Thirteen of the 24 patients were cured using appropriate antibiotics (true infection group); however, 11 of the 24 patients were cured using inappropriate antibiotic therapy or no antibiotics (contamination group). Malignancy and neutropenia significantly increased the odds of true C. striatum bloodstream infection. CONCLUSIONS: The Corynebacterium species is often considered a contaminant when isolated in culture. Instead, particularly when the strain is isolated from blood, the species should be considered clinically relevant and identified to the species level; in addition, antimicrobial susceptibility testing is recommended.

BACKGROUND: A single 20-mg dose of inhaled laninamivir octanoate is an effective treatment of influenza. However, the efficacy of laninamivir octanoate for the prevention of influenza in children <10 years of age has not yet been established. METHODS: We conducted a double-blind, multicenter, randomized, placebo-controlled study to determine whether the efficacy of a single 20-mg dose of inhaled laninamivir octanoate to prevent the development of influenza was superior to that of placebo as prophylaxis for influenza in pediatric (<10 years) household members of index cases. Eligible subjects without influenza, in contact with an influenza-infected index case living in the same household, were blindly randomly assigned in a 1:1 ratio to receive 20 mg of laninamivir octanoate or placebo. The primary end point was the proportion of subjects who developed clinical influenza during a 10-day period. RESULTS: A total of 343 subjects were randomly assigned, with 341 subjects included in the full analysis set for the primary analysis. The proportions of subjects who developed clinical influenza were 11% (18/171) in the laninamivir octanoate group and 19% (33/170) in the placebo group (P = .02). The relative risk reduction was 45.8% (95% confidence interval, 7.5% to 68.2%). The incidence of adverse events was similar in both groups. CONCLUSIONS: A single 20-mg dose of inhaled laninamivir octanoate was effective and well tolerated as prophylaxis for influenza.

Point-of-care testing for Mycoplasma pneumoniae infection may be ideal and useful because significant numbers of the cases will be seen as outpatients. Recently, a new immunochromatographic method (ICM) targeting M. pneumoniae ribosomal protein L7/L12 (RP-L7/L12) in pharyngeal swabs became available in Japan, although clinical data and basic information regarding efficacy and characterization of this ICM are limited. The present study examined the fate of M. pneumoniae RP-L7/L12 during in vitro growth and the correlation between M. pneumoniae concentration in clinical specimens and the sensitivity of the ICM test. The usefulness of the ICM was investigated in patients suspected of having M. pneumoniae pneumonia and upper respiratory tract infection (137 children and 39 adults). The limit of detection for the ICM test was 1.1×104 c.f.u. ml-1 of M. pneumoniae. Bacterial production of RP-L7/L12 correlated positively with the viable M. pneumoniae concentration in vitro; antigen was then degraded in culture broth, with an in vitro half-life of approximately 2 days. Five other Mycoplasma spp. and 14 representative respiratory pathogens were ICM assay negative at bacterial concentrations of 106 c.f.u. ml-1. The clinical sensitivity and specificity of the ICM assay were 57.1 % (20/35) and 92.2 % (130/141), respectively, in comparison with bacterial culture. Clinical specimens containing ≥106 c.f.u. ml-1 of M. pneumoniae burden were ICM positive in 13 of 18 cases (72.2 %). The ICM is a poorly sensitive but reasonably specific means for detecting M. pneumoniae infections.

Human metapneumovirus (hMPV) is known as one of popular agents of acute respiratory infection in children. We reviewed the patients' background, result of initial blood test, bacterial culture, chest X-ray and clinical features of hospitalized children with lower respiratory tract infections caused by hMPV from March 2014 to February 2015 and compared them with the infections due to respiratory syncytial virus (RSV) and other causative agents. Of 419 patients tested by rapid virus antigen tests, 35 were positive for hMPV, 145 were positive for RSV, and 239 were negative for both viruses. Most of hMPV infections occurred between March and June, and 72% of households of hMPV-positive children got sick. hMPV-positive children did not have any specific symptoms such as wheezing in RSV- positive children. However, many of them were admitted due to prolonged high fever and/or ill appearance despite of no respiratory distress. Although it is said that hMPV-positive children admitted to hospitals tend to have pneumonia, the ratio of children'with pneumonia in this study was less than 60%.

To our knowledge, this is the first report of the use of real-time reverse transcription-polymerase chain reaction to assess changes in viral load in a patient with congenital rubella syndrome (CRS). Rubella-specific antibody titers were also determined. The patient was a male neonate born to a primipara with rubella infection at 10 weeks of gestation. He had no symptoms at birth, but rubella virus was detected in his pharynx, blood, and urine. His mental and physical development was normal for 1 year; however, he was diagnosed with deafness at 13 months of age. Thus, the patient was diagnosed with CRS. Rubella infection in the pharynx was almost constant until 5 months of age; however, it increased dramatically at 6 months of age. No infection was detected at 13 months. Rubella-specific immunoglobulin M titer was consistently low until 9 months of age and then decreased gradually until it became negative at 20 months of age. Rubella-specific immunoglobulin G titer was high at birth. However, it decreased at 3 months and increased again at 4 months. This titer peaked at ∼9 months and then decreased again at 13 months. This case shows that the period after the decline in maternal antibody titers, not the neonatal period, may be the most contagious period in patients with CRS.

A 16-year-old boy with chronic granulomatous disease presented with pneumonia and rib osteomyelitis. Emericella nidulans var. echinulata was isolated from his sputum. After starting voriconazole, Rasamsonia piperina was isolated from the rib swelling. A combination therapy of voriconazole and micafungin effectively eradicated this invasive mixed-mold infection. In immunocompromised patients, a precise pathogenic diagnosis is clinically useful for administration of an appropriate treatment regimen.

We report an 8-year-old patient with catheter-related bacteremia caused by linezolid-resistant Staphylococcus epidermidis that was isolated after the long-term, repeated use of linezolid. Three S. epidermidis strains isolated from this patient were bacteriologically analyzed. While the strain isolated prior to linezolid initiation was susceptible to linezolid, two strains after linezolid therapy displayed low-level linezolid susceptibility (MIC, 4 mg/L) and linezolid resistance (MIC, 16 mg/L). T2500A mutation in two copies and G2575T mutations in three copies of 23S rRNA were detected in the low-susceptible strain and the resistant strain, respectively. Linezolid-resistant S. epidermidis infection is rare, but may occur with the long-term administration of linezolid.

Heptavalent pneumococcal conjugate vaccine (PCV7) was introduced to Japan in 2010. We investigated the impact of PCV7 on childhood community-acquired pneumonia (CAP) and pneumococcal pneumonia (PP). Children aged &lt; 5 years living in Chiba city, Japan, who were admitted to hospitals were enrolled to estimate the incidence of CAP based on the mid-year population. PP was determined by the presence of Streptococcus pneumoniae in cultured blood and/or sputum samples of CAP patients. The incidence of CAP and S. pneumoniae isolated from PP patients was compared before (April 2008-March 2009) and after (April 2012-March 2013) the introduction of PCV7 immunization. The annual incidence of CAP was reduced [ incidence rate ratio 0.81, 95% confidence interval (CI) 0.73-0.90]. When comparing post-vaccine with pre-vaccine periods, the odds ratio for PP incidence was 0.60 (95% CI 0.39-0.93, P = 0.024). PCV7-covered serotypes markedly decreased (66.6% in pre-vaccine vs. 15.6% in post-vaccine, P &lt; 0.01), and serotypes 6C, 15A, 15C and 19A increased. Multidrug-resistant international clones in the pre-vaccine period (Spain(6B)-2/ST90, Taiwan(19F)-14/ST236) decreased, while Sweden(15A)-25/ST63 was the dominant clone in the post-vaccine period. A significant reduction in the incidence of both CAP hospitalizations and culture-confirmed PP of vaccine serotypes was observed at 2 years after PCV7 vaccination.

症例:32歳、外国人女性、肺結核の治療歴あり。経過:妊娠初期の喀痰検査で塗抹陰性、培養でMycobacterium tuberculosis陽性となり、多剤耐性菌と判明したため、当院を紹介受診した。経過中に気道症状なく、画像上も変化を認めなかった。妊娠中、結核治療は行わなかった。児は帝王切開で出生し、出生後は隔離管理を行った。児の先天性結核は認めず、児への予防投薬は行わなかった。母の治療開始まで母児隔離が望ましかったが現実的には困難であった。事前のスタッフへの空気感染対策指導により、施設内感染は認めなかった。まとめ:耐性菌であったことから治療の点や家族背景、言葉の面で対応に苦慮した。多剤耐性結核、超多剤耐性結核といった薬剤耐性結核菌が世界で問題になっている。今後、同様の症例の増加が懸念されるため国内における体制整備が必要である。(著者抄録)

Streptococcus pneumoniae is the major causal pathogen of otitis media, pneumonia, and invasive pneumococcal diseases, such as sepsis and meningitis, in children. More than 95 different polysaccharide capsule types have been identified. Nontypeable strains (NTs) causing an invasive pneumococcal disease are rare, but there are not a few otitis media and sinusitis, the respiratory tract infectious disease caused by NTs [1,2]. In this study, we compared the difference of microtiter biofilm assay (MBA) and biofilm morphology between typeable strains and NTs. The biofilm morphology of a typeable strain, sero type 24 F, and a NT strain were observed by scanning electron microscopy (SEM). A 1 × 1.5 cm polystyrene piece was placed in a culture dish, filled with THYB, and cells were cultured for 18 h at 37°C in 5% CO2. Specimens were fixed with 2.5% glutaraldehyde, post-fixed with 1% OsO4, dehydrated with graded ethanol, and substituted with t-butyl alcohol. They were freeze-dried in VFD-21S t-butyl alcohol freeze-drying apparatus (Vacuum Device Co. Ltd., Mito, Japan) and coated with platinum-palladium in an ion spatter E-102 (Hitachi, Tokyo), and observed in an S-3400N scanning electron microscope (Hitachi, Tokyo) at 10 kV. Mature biofilms were observed in nontypeable strains, but no biofilm was observed in typeable strain by SEM.

B型インフルエンザの流行が主体であった2013/2014シーズン後半にノイラミニダーゼ阻害薬を処方した16歳以下の206例を対象とし、発熱遷延例の状況を中心に臨床効果を比較検討した。投与薬剤はラニナミビル24例、ザナミビル83例、オセルタミビル99例であり、治療開始後の平均有熱期間はラニナミビル、オセルタミビル、ザナミビルの順で36.6時間～42.2時間の間に収まっていた。発熱遷延例はB型に多くみられたが、年齢・ワクチン接種歴・細菌二次感染などの有意な要因は認めず、インフルエンザワクチン接種の有無と罹患した型に明らかな関係はなかった。また、服薬、吸入コンプライアンスはいずれの群も良好で各薬剤の副作用に差は認めなかった。

We studied the molecular evolution of the C-terminal 3rd hypervariable region in the attachment glycoprotein gene of human respiratory syncytial virus subgroup B (HRSV-B) genotypes BA9 and BA10. We performed time-scaled phylogenetic analyses using Bayesian Markov chain Monte Carlo methods. We also performed a genetic distance analysis (p-distance analysis), positive and negative selection analyses, and a Bayesian skyline plot (BSP) analysis. We found that genotype BA9 diverged from the common ancestor of genotypes BA7, BA8, and BA10, while genotype BA10 diverged from the ancestor of genotypes BA7 and BA8. Strains of both genotypes were distributed worldwide. BA9 and BA10 diverged between 1999 and 2001. Both BA9 and BA10 evolved rapidly (about 4.8×10(-3)substitutions/site/year) and formed three distinct lineages in a 10-year period. BA10 strains belonging to lineage 3 had large genetic distances (p-distance>0.07). Thus, it may be possible to classify these strains as a new genotype, BA11. No positive selection site was detected in either genotype. Phylodynamic analyses showed that the effective population size of BA10 decreased gradually since 2010 and BA9 slightly decreased since 2009. The results suggested that the recently prevalent HRSV-B genotypes BA9 and BA10 evolved uniquely, leading to epidemics of HRSV-B worldwide over a 15-year period.

We investigated the clinical symptoms of 206 pediatric patients with influenza virus infection and compared them among oseltamivir-treated, zanamivir-treated, and laninamivir-treated groups in 2013/2014 influenza season. The drug compliance of each neuraminidase inhibitor was good in all three groups. Although the duration of fever after administration of the first dose of each neuraminidase inhibitor were significantly prolonged in the patient with influenza B infection than in the patient with influenza A infection, no statistically significant difference in the clinical efficacy and the side effect among three groups were found. The number of biphasic fever episodes in patients treated with neuraminidase inhibitor was rare (two episodes of oseltamivir-treated group and one episode of zanamivir-treated group). In conclusion, under the good drug compliance, the efficacy of all three neuraminidase inhibitor was the same for the treatment of influenza virus infection in children.

BACKGROUND: In Japan, the seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in 2010. PCV13 has replaced PCV7 since November 2013. METHODS: The effectiveness of PCV7 in protecting against invasive pneumococcal disease (IPD) in children aged <5 years was evaluated in a nationwide active population-based surveillance of IPD in 2008-2013 in 10 prefectures in Japan. RESULTS: 1181 cases were identified; 711 pneumococcal strains were analyzed for serotyping and antimicrobial resistance. Compared with the baseline IPD incidence (25.0 per 100,000), a 98% decline in IPD caused by PCV7 serotypes was found after the introduction of PCV7. This was partially offset by an increased incidence of IPD caused by PCV13 minus PCV7 and non-PCV13 serotypes, resulting in a 57% decline in overall IPD incidence. Absolute increases in the incidence rates of IPD caused by PCV13 minus PCV7 and non-PCV13 serotypes were 2.1 and 2.8 per 100,000 during the study period, respectively. The proportion of meropenem-nonsusceptible strains, especially with serotypes 19A and 15A, increased significantly after PCV7 introduction. CONCLUSIONS: Our data confirmed a 98% decline in IPD incidence caused by PCV7 serotypes in children aged <5 years and serotype replacement after PCV7 introduction. This shows the importance of continuing surveillance of serotypes responsible for IPD and their antimicrobial resistance in Japan.

The antifungal agents approved in Japan for pediatric use are limited and many unapproved drugs are actually used without clear instruction for dosage. We investigated the pharmacokinetics of caspofungin for the treatment of invasive candidiasis and invasive aspergillosis in 20 Japanese pediatric patients using a pediatric-specific dosage based on body surface area. Caspofungin was administered intravenously over 60 min as 70 mg/m(2) on Day 1, followed by 50 mg/m(2) per day. Five or 4 point blood sampling were done in 15 patients on Day 4-5 to calculate AUC0-24 h. The geometric means (95% confidence interval) of C24 h and AUC0-24 h in the pediatric patients were 3.3(2.5, 4.4) μg/mL and 175.1 (139.3, 220.1) μg hr/mL, respectively, which were comparable to those in Japanese adult patients [3.2 (2.8, 3.5) μg/mL and 144.9 (131.7, 159.3) μg hr/mL, respectively]. Among the 20 patients, 10 (50%) had at least 1 drug-related adverse event which was considered related to caspofungin therapy. No drug-related serious adverse event and no death occurred. The most common drug-related adverse events were events relating to hepatic function (mainly increases in ALT and AST). The overall success in efficacy was observed in 13 of 20 patients. In conclusion, once daily administration of caspofungin (70 mg/m(2) on Day 1, followed by 50 mg/m(2) [maximum daily dose not to exceed 70 mg]), which is the same dosage being used in overseas, achieved sufficient drug exposure and a favorable efficacy and acceptable safety profile in Japanese pediatric patients with invasive fungal infections.

7価肺炎球菌結合型ワクチン(PCV7)導入後の侵襲性肺炎球菌感染症(IPDs)の血清型の変化が欧米から報告されている。わが国でも2011年に公費負担となり、2013年11月からは13価肺炎球菌結合型ワクチン(PCV13)が導入された。わが国でのPCV7導入後の血清型の推移を検討した報告は少なく、PCV7導入後の血清型の推移を明らかにするため検討を行った。当センターで2010年3月〜2014年3月までに検出されたIPDsのうち、危険因子、ワクチン歴、臨床診断、血清型に関して検討を行った。IPDsは45例で、基礎疾患としてIPDsの危険因子をもつ児は29%(13/45)、ワクチン接種者は29%(13/45)であった。臨床診断は、潜在性菌血症26例、肺炎12例、細菌性髄膜炎4例、眼窩蜂窩織炎2例、化膿性リンパ節炎1例であった。PCV7含有血清型、およびPCV13含有血清型は33%(15/45)、56%(25/45)で検出された。PCV7ワクチン接種者は、PCV7含有血清型での罹患は認めなかった。またPCV7導入後、PCV7含有血清型によるIPDsは、年次ごとに統計学的に有意に減少した(p<0.001)、今回の検討でPCV7の有効性が示された一方、PCV13の導入前にもかかわらず、PCV13非含有血清型が44%とワクチン非含有血清型が多くみられることがわかった。PCV13導入後もIPDsの血清型の推移を観察していく必要がある。(著者抄録)

In Japan, publicly subsidized Haemophilus influenzae serotype b vaccines became available in 2011; consequently, the incidence of invasive H. influenzae infection in paediatric patients of less than 5 years of age decreased dramatically. In 2013, the first case of H. influenzae serotype f (Hif) meningitis in a Japanese infant was reported, and another case of Hif meningitis in a Japanese infant was observed in 2013. We experienced a fatal paediatric case of Hif bacteraemia in 2004; therefore, we conducted an analysis of the three Hif strains isolated from these three Japanese children with invasive Hif infections. All three strains were β-lactamase-non-producing, ampicillin-sensitive strains, with MICs of 1 µg ml(-1) or less. However, one of the three strains showed slightly elevated MICs for ampicillin (1 µg ml(-1)), cefotaxime (0.25 µg ml(-1)) and meropenem (0.13 µg ml(-1)). A molecular analysis by multilocus sequence typing identified all three strains as sequence type (ST) 124, which is a predominant invasive Hif strain in many countries. SmaI-digested PFGE showed variable DNA fragmentation patterns among the strains, suggesting that some highly virulent strains have originated from a single ST124 clone and caused invasive Hif infections in Japan. Additional studies are needed to determine the factors that have led to the clonal expansion of virulent ST124 strains.

OBJECTIVES: Linezolid has been reported to remain active against 98% of staphylococci with resistance identified in 0.05% of Staphylococcus aureus and 1.4% of CoNS. The objective of this study was to characterize the linezolid-resistance mechanisms in the linezolid-resistant CoNS strains isolated in Japan. METHODS: Staphylococcus capitis strains exhibiting linezolid MICs >8 mg/L isolated from inpatients between 2012 and 2014 were screened for cfr and mutations in 23S rRNA, L3 and L4 by PCR/sequencing. Isolates were also examined for mutations in the rlmN gene. RESULTS: S. capitis had six 23S rRNA alleles. Five S. capitis isolates displayed linezolid MICs of 8, 16 and 32 mg/L. G2576U mutations were detected in three, four or five copies of 23S rRNA in all isolates. In two isolates exhibiting the highest linezolid MIC (32 mg/L) there was a large deletion in a single copy of 23S rRNA. Repeated 10 bp sequences were found in both 16S and 23S rRNAs, suggesting deletion by recombination between the repeats. One isolate had the mutation Ala-142→Thr in the ribosomal protein L3. All linezolid-resistant isolates also demonstrated mutations in the gene encoding RlmN methyltransferase, leading to Thr-62→Met and Gly-148→Ser. CONCLUSIONS: Multiple mechanisms appeared to be responsible for the elevated linezolid resistance in S. capitis isolates: a G2576U mutation in different numbers of copies of 23S rRNA, loss of a single copy of 23S rRNA and a mutation in the ribosomal protein L3, suggesting the accumulation of independent mutational events.

We analyzed non-serotype b encapsulated Haemophilus influenzae (non-b Hi) isolated from pediatric patients at Chiba Children's Hospital during 2000-2012. Among 3,532 clinical isolates of H. influenzae, there were 57 (1.6%) strains of non-b Hi, 152 (4.3%) of serotype b H. influenzae (Hib), and 3,323 (94.1%) of non-typeable H. influenzae (NTHi). Fifty-seven strains of non-b Hi were serotyped useing the slide agglutination test and PCR. Twenty-nine strains were identified as type e (Hie) and 28 as type f (Hif), and the results according to the slide agglutination test and PCR were completely identical. Whereas 52 of 57 strains (91.2%) were isolated from respiratory specimen, only one Hif strain (1.8%) was isolated from a sterile site. There were 47 (82.4%) β-lactamase-non-producing ampicillin (ABPC)-sensitive strains (BLNAS), 5 (8.8%) β-lactamase-producing strains (BLP), and only 1 (1.8%) β-lactamase-non-producing ABPC-resistant strain (BLNAR). Thus the frequency of non-b Hi was lower than that of Hib. The source of non-b Hi was similar to that of NTHi, which was mainly isolated from respiratory specimen. Antimicrobial resistant pattern of non-b Hi was different from that of Hib in which the frequency of BLP was relatively high, and NTHi in which that of BLNAR was high. An increase of invasive H. influenzae infections caused by NTHi, Hie, and Hif was reported in the countries where Hib vaccine had been widely used. Because it is assumed that invasive non-Hib infection will be predominant in the near future in Japan, serotyping of invasive strains is crucial. Continuous monitoring of distribution of non-b Hi in the clinical isolates of H. influenzae is also important.

No studies showed specific antibody levels against all serotypes covered by 13-valent pneumococcal conjugate vaccine (PCV13) among polyclonal intravenous immunoglobulin (IVIG) products. Our study aimed to assess whether we could expect the efficacy of IVIG therapy for invasive pneumococcal disease (IPD) and to clarify the age group which should be recommended for IVIG therapy in case of IPD. Serotype-specific immunoglobulin G (IgG) levels against PCV13 serotypes were measured in four IVIGs which were produced from Japanese donors who were not immunized with any pneumococcal conjugate vaccines (PCVs), and in the serum of 160 non-PCV immunized Japanese subjects, by enzyme-linked immunosorbent assay. The functional opsonic activities of the IVIGs against serotypes 6B and 19A were assessed by a multiplexed opsonophagocytic killing assay. Japanese infants aged <2 years had a geometric mean IgG concentration of <0.35 μg/ml against several serotypes. Serotype-specific IgG concentrations varied among IVIGs. In general, IgG antibodies against serotypes 6A, 14 and 19A were higher in each IVIG. Although opsonization indices also varied among preparations, each IVIG had the ability to opsonize both serotypes 6B and 19A. This study suggests that routine immunization with PCV is important for prevention of IPD, especially for children <2 years old and IVIGs might be effective for IPD patients.

2008年6月～2012年5月までに不明熱で当科入院となった20症例を後方視的に検討した。20例中CT 18例、67Gaシンチ13例、骨髄検査14例で施行されたが、診断に寄与したのはCT 3例、67Gaシンチ0例、骨髄検査2例であった。なお、骨髄検査で異常を示した症例は血算にて2系統以上の血球減少やLDH高値を認めていた。不明熱精査でも、血算のように広く行われる検査を丁寧にみていくことが重要である。(著者抄録)

The Haemophilus influenzae type b (Hib) vaccine and the heptavalent pneumococcal conjugate vaccine (PCV7) were introduced in Japan in 2008 and 2010, respectively. In 2011, immunization with these two vaccines was encouraged throughout Japan through a governmental program. Children treated in Chiba prefecture for culture-proven invasive H. influenzae disease (IHiD) and invasive Streptococcus pneumoniae disease (IPD) were identified in a prefectural surveillance study from 2008 to 2013. The incidence rate ratio (IRR) and its confidence interval (CI) were calculated to compare the 3 years before and after governmental financial support for vaccination. The average number of IHiD and IPD cases among children <5 years of age in 2011-2013 decreased 84% (IRR: 0.16, 95% CI: 0.09-0.26, p<0.0001) and 51% (IRR: 0.49, 95% CI: 0.37-0.63, p<0.0001) compared with those occurring in 2008-2010. The most common non-PCV7 serotype encountered in 2011 and 2013 was 19A. After governmental subsidization of Hib and PCV7 vaccination, IHiD and IPD decreased in Chiba prefecture, Japan. Continuous surveillance is necessary to determine the effectiveness of these two vaccines and for detection of emerging invasive serotypes.