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Objectives　At the beginning of the COVID-19 pandemic, the number of infected children was lower than that of adults. Most cases were transmitted in the family, asymptomatic, and severe cases were rare. In the sixth wave in Japan the number of infected children increased sharply after the Omicron variant had been replaced in December 2021, which had a substantial influence in maintaining social and medical functions. Furthermore, few reports on child death in the country have raised concerns among parents. However, no literature has elucidated the epidemiological characteristics of the Omicron variant in children. In this study, we aimed to clarify them during the sixth wave in Japan.Methods　We analyzed the data of 28,086 COVID-19-infected patients those were registered in the Yamashirokita Public Health Center between January 15, 2022 and May 31, 2022. The cumulative incidence and hospitalization rate were compared between the age groups <15 and those >15 years based on the databases compiled by our public health center and the Kyoto prefecture government. In addition, we analyzed the background, length of hospitalization, and clinical symptoms of 24 patients based on active epidemiological investigation, health observations, and discharge reports submitted from medical facilities.Results　Of the 52,897 residents <15 years (pediatric population is 12.3%), 15.1% (7,980 cases) were infected, and children accounted for 28.4% of all-age infected patients. Among them, 24 were hospitalized (0.3% of children with COVID-19, 0.04% of the child population). Conversely, of the 377,093 residents aged ≥15 years, 5.3% (20,106 patients) were infected. Among them, 1,088 were hospitalized (5.4% of COVID-19 patients, 0.28% of the adult population). For 24 hospitalized children, 22 (91.6%) had mild cases and 2 (8.3%) had moderate cases, and no severe case was noted based on the criteria of severity in Japan's COVID-19 medical care guidelines. Two patients (8.3%) were hospitalized for treatment of other diseases. The median of hospital stay was 3.5 days, and 20 patients (83.3%) were discharged home during the recuperation period.Conclusions　The cumulative incidence of children with COVID-19 in the sixth wave was 15.1%, approximately three times higher than that of the older patients; however, no severe case was observed in children.

Respiratory quinolones (RQs) are broad-spectrum antimicrobial agents used for the treatment of a wide variety of community-acquired and nosocomial infections. However, bacterial resistance to quinolones has been on the increase. In this study, we investigated the predicted efficacy of RQs for various strains of 9 bacterial species clinically isolated at our university hospital using the Monte Carlo simulation (MCS) method based on pharmacokinetics/pharmacodynamics modeling. In addition, the influence of the patients' renal function on the efficacy of RQs was evaluated. We surveyed antimicrobial susceptibility testing of 9 bacterial species (n = number of strains) [Streptococcus pneumoniae (n = 15), Streptococcus pyogenes (n = 14), Streptococcus agalactiae (n = 19), methicillin-susceptible Staphylococcus aureus (MSSA) (n = 24), Escherichia coli (n = 35), Haemophilus influenzae (n = 17), Klebsiella pneumoniae (n = 14), Pseudomonas aeruginosa (n = 31), and Moraxella catarrhalis (n = 11)] to 4 RQs [garenoxacin (GRNX), levofloxacin (LVFX), sitafloxacin (STFX), and moxifloxacin (MFLX)]. We found that compared with the other RQs, Gram-positive cocci was most resistant to LVFX, and that the minimum inhibitory concentration (MIC₉₀) values for S. pneumoniae, S. pyogenes, S. agalactiae, and MSSA were high (2, 16, > 16, and 8 µg/mL, respectively). In regard to Gram-negative rods, the susceptibility of E. coli to RQs was found to be decreased, with the MIC₉₀ values of GRNX, LVFX, STFX, and MFLX being > 16, 16, 1, and 16 µg/mL, respectively. MCS revealed that the target attainment rate of the area under the unbound concentration-time curve divided by the MIC₉₀ (ƒ · AUC/MIC ratio), against S. pneumoniae was 86.9-100%, but against E. coli was low (52.1-66.2%). The ƒ · AUC/MIC target attainment rate of LVFX against S. pneumoniae, S. pyogenes, and S. agalactiae tended to decrease due to increased creatinine clearance, and that of LVFX and STFX against MSSA also tended to decrease. The findings of this study suggest that the drug susceptibility distribution of each RQ varies, even within the same bacterial species, and that the expected efficacy also varies between the drugs. Moreover, the influence of the patient's renal function on the efficacy differed among the 3 renal excretory drugs (GRNX, LVFX, and STFX), thus suggesting that the efficacy also differs. In conclusion, the findings of this study show that for the administration of RQs, it is desirable to select agents in consideration of surveyed sensitivity within the population and the pharmacokinetic characteristics.

Case 1: A man in his sixties underwent extended right lobectomy of the liver for hepatic hilar cholangiocarcinoma (stage III, fCur B)in July2002. CT scans revealed cancerous pleuritis in March 2005, and he was treated with the chemotherapy of GEM alone as first-line, combined chemotherapy of S-1 and GEM as second-line, and CDDP and GEM as third-line treatment. These therapies have been effective for about 20 months. Case 2: A woman in her sixties was diagnosed with advanced gallbladder cancer(stage IVb)in September 2005. She was given combined chemotherapy of S-1+GEM as first-line, and CDDP+GEM as second-line treatment. The main tumor and metastatic lymph nodes were shrunk, allowing us to perform extended hepatectomy. Histopathologic examinations of the resected specimen of the liver involved by the tumor showed the increased infiltration of inflammatorycells and fibrosis. These patients have been managed on an outpatient basis with good QOL and cancer controlled. Although there has been no established standard regimen, the combined chemotherapy based on GEM will be a provisional standard regimen for patients with advanced biliarytract cancers.

A 71-year-old man underwent right hemicolectomy for an ascending colon cancer (stage II, Cur A) in September 2001. Adjuvant chemotherapy with tegafur/uracil was performed, but CT scans and FDG-PET, conducted in May 2003, revealed cancerous pleuritis and lung metastasis. Although 2 courses of the chemotherapy with LV+5-FU (RPMI regimen) were completed, progressive disease was confirmed. Therefore, the chemotherapy with CPT-11 (100 mg/ day; day 1, 15)+S-1 (100 mg/day; day 1-21) was started in May 2004. After completion of 6 courses, CT scan showed a partial response. Only grade 2 vomiting was noted as an adverse reaction to the treatment, however, the patient has been managed on an outpatient basis for the last 3 years with good QOL and the cancer under control. This case suggests that this combination therapy can be expected to be highly effective as a safe approach for continuously maintaining the QOL of patients with advanced or recurrent colorectal cancer.

A 70-year-old woman was admitted to our hospital for evaluation of a nodular shadow and an apparent cavity in the right middle lung field. Transbronchial biopsy and percutaneous needle biopsy had failed to result in a diagnosis. Serial chest X-ray films revealed slight regression of the nodule without therapy. Pulmonary dirofilariasis was diagnosed after open-lung biopsy and Ouchterlony's double diffusion test. Cavity formation and spontaneous regression are rare in pulmonary dirofilariasis.