In a pandemic crisis where we must face an unknown infectious disease, it is necessary to accurately and rapidly assess the immune status of individuals or groups in real-time against the causative microorganisms. Nevertheless, in the current COVID-19 pandemic, SARS-CoV-2 antibody testing requires serum or plasma collected by venipuncture. However, this sample collection poses several logistical restrictions, such as the requirements of venipuncture by trained phlebotomists with direct contact, immediate storage in a refrigerator or freezer after collection, and cold chain transport to maintain the integrity of the biospecimen. In contrast, dried blood spot (DBS) sampling is simple and inexpensive; DBS samples can be self-collected and remain stable at ambient temperature until sent by postal mail to a laboratory for processing. Moreover, DBS sampling has the potential to provide a widely available solution for assessing and tracking herd immunity in various populations, including those in low- and middle-income countries, without geographic limitations. The present study is the first to demonstrate the correlations between neutralizing antibody responses not only against the wild-type strain but also BA.5 and XBB.1.5 in the DBS eluate and paired sera. In addition, neutralizing antibodies have been shown to remain stable in collected DBS transported at HT (40°C) for one month, following one-month storage at room temperature. However, in our experiments, the correlations and stability over time and temperature varied depending on the type of filtered papers used, with filter paper no. 545 being the most suitable for DBS cards in the high-throughput chemiluminescent reduction neutralizing test (htCRNT) assay. Evaluating neutralizing antibodies using DBS eluates could be applied to other pathogens and in future pandemics, enabling reliable and affordable seroepidemiological surveillance, even in remote areas and low-income countries.

To investigate the safety and effectiveness of colistin (Aldreb^®, hereinafter referred to as “this drug”) under actual use conditions in Japan, a drug use investigation was conducted using the all-case investigation method. The subjects were patients who were diagnosed with infection and received this drug for the first time, and the observation period was from the day that administration of this drug was started to the day that it was discontinued or completed. Regarding safety, the development of adverse reactions was evaluated. Regarding effectiveness, global assessment was performed by physicians in charge of the investigation, and the susceptibility of causative bacteria to colistin were evaluated. Between May 25, 2015 and September 20, 2022, 815 patients were enrolled. Case report forms were collected from 282 patients who were enrolled by October 31, 2017. There were 280 patients in the safety analysis set and 169 patients in the effectiveness analysis set. In terms of preventing nephrotoxicity and the emergence of resistant bacteria, the package insert mentions dosage adjustment based on creatinine clearance and the testing of the colistin susceptibility of causative bacteria. However, among 262 patients in the safety analysis set whose creatinine clearance was measured before the administration of this drug was started, no dosage adjustment based on creatinine clearance (as described in the package insert of this drug) was performed in 34.4% of the patients (90/262 patients), and among 261 patients in whom this drug was used for appropriate bacterial species, no colistin susceptibility testing was performed in 26.4% (69/261 patients).The total number of days (mean ± standard deviation) on which this drug was administered to patients in the safety analysis set was 13.9±18.08 days, and adverse reactions were observed in 32.5% (91/280 patients).The proportion of patients who developed adverse reactions related to safety specifications, i.e., “renal impairment,” “neurotoxicity,” and “pseudomembranous colitis,” was 27.1% (76/280 patients), 2.9% (8/280 patients), and 0.4% (1/280 patients), respectively. In the effectiveness analysis set of 169 patients, the drug was effective in 75.1% (127/169 patients) according to global assessment by the physicians in charge. The results of this investigation found no new problem with the safety and effectiveness of this drug under the actual use conditions. We thought that in terms of preventing nephrotoxicity and the emergence of resistant bacteria, it is important to properly use this drug as indicated in the package insert of this drug and “Practical guide for appropriate use of colistin: update.”