Analysis of Suspected Measles Cases with Discrepant Measles-Specific IgM and rRT-PCR Test Results, Japan.

We investigated clinically suspected measles cases that had discrepant real-time reverse transcription PCR (rRT-PCR) and measles-specific IgM test results to determine diagnoses. We performed rRT-PCR and measles-specific IgM testing on samples from 541 suspected measles cases. Of the 24 IgM-positive and rRT-PCR--negative cases, 20 were among children who received a measles-containing vaccine within the previous 6 months; most had low IgG relative avidity indexes (RAIs). The other 4 cases were among adults who had an unknown previous measles history, unknown vaccination status, and high RAIs. We detected viral nucleic acid for viruses other than measles in 15 (62.5%) of the 24 cases with discrepant rRT-PCR and IgM test results. Measles vaccination, measles history, and contact history should be considered in suspected measles cases with discrepant rRT-PCR and IgM test results. If in doubt, measles IgG avidity and PCR testing for other febrile exanthematous viruses can help confirm or refute the diagnosis.

Isolation and whole-genome sequencing analysis of Escherichia fergusonii harboring a heat-labile enterotoxin gene from retail chicken meat in Okinawa, Japan.

This study aimed to reveal the prevalence of heat-labile enterotoxin (LT) gene-positive Escherichia fergusonii in retail chicken meat and genetically characterize these strains. E. fergusonii harboring LT gene was isolated from 6 out of 60 (10%) retail chicken samples in Okinawa, Japan. Whole-genome sequencing analysis revealed that LT gene-positive E. fergusonii from chicken meat and feces contain an IncFII plasmid harboring elt1AB, and suggested to spread clonally to retail chicken through fecal contamination. Additionally, it was found that these strains harbor multidrug-resistant genes on their plasmids. Their pathogenicity and continuous monitoring are required for confirmation.

Molecular evolution of VP3, VP1, 3C(pro) and 3D(pol) coding regions in coxsackievirus group A type 24 variant isolates from acute hemorrhagic conjunctivitis in 2011 in Okinawa, Japan.

A large acute hemorrhagic conjunctivitis (AHC) outbreak occurred in 2011 in Okinawa Prefecture in Japan. Ten strains of coxsackievirus group A type 24 variant (CA24v) were isolated from patients with AHC and full sequence analysis of the VP3, VP1, 3C(pro) and 3D(pol) coding regions performed. To assess time-scale evolution, phylogenetic analysis was performed using the Bayesian Markov chain Monte Carlo method. In addition, similarity plots were constructed and pairwise distance (p-distance) and positive pressure analyses performed. A phylogenetic tree based on the VP1 coding region showed that the present strains belong to genotype 4 (G4). In addition, the present strains could have divided in about 2010 from the same lineages detected in other countries such as China, India and Australia. The mean rates of molecular evolution of four coding regions were estimated at about 6.15 to 7.86 × 10(-3) substitutions/site/year. Similarity plot analyses suggested that nucleotide similarities between the present strains and a prototype strain (EH24/70 strain) were 0.77-0.94. The p-distance of the present strains was relatively short (<0.01). Only one positive selected site (L25H) was identified in the VP1 protein. These findings suggest that the present CA24v strains causing AHC are genetically related to other AHC strains with rapid evolution and emerged in around 2010.

Severe Fever with Thrombocytopenia Syndrome Virus RNA in Ticks from Wild Mongooses in Okinawa Prefecture, Japan.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic tick-borne disease caused by SFTS virus (SFTSV). SFTSV has a wide spectrum of animal hosts and is considered to circulate in an enzootic tick-vertebrate-tick cycle. A previous seroepidemiological study showed the presence of anti-SFTSV antibodies in wild mongooses (Herpestes auropunctatus) and indicated that outdoor activity was associated with an increased risk of tick bites among Okinawa residents. However, the association of SFTSV with wild mongooses and ticks remains unclear. To understand the association between ticks and mongooses with respect to the SFTSV enzootic cycle, we investigated the presence of SFTSV RNA in ticks collected from wild mongooses on the Okinawa Island. A total of 638 ticks belonging to 2 genera and 3 species (Haemaphysalis hystricis, Haemaphysalis formosensis, and Ixodes granulatus) were collected from 22 wild mongooses from 2016 to 2021. SFTSV RNA was detected in two pools of H. hystricis larvae collected from a wild mongoose in the central area of the main island of Okinawa in 2017. Although the prevalence of SFTSV in ticks from wild mongooses is low, endemic circulation of the virus in Okinawa should be carefully monitored to prevent future infections.

Characteristics of Household Transmission of COVID-19 during Its Outbreak in Okinawa, Japan from February to May 2020.

The Okinawa prefecture confirmed 142 cases of coronavirus disease from February 14 to May 2020. Among them, 78 were the first cases of a household with 174 household contacts. Of the 174 contacts, 21 contracted the disease, indicating a secondary attack rate of 12.1% (95% confidence interval [CI] 7.6-17.9%). No significant differences were observed in the demographics and quantitative reverse transcription-polymerase chain reaction test results between the first cases that became the sources of infection to the household members. The secondary attack rates with respect to the various characteristics of the household members were significantly different: aged >69 years (40.9% [95% CI 20.7-63.6%]) and those with underlying diseases (36.0% [95% CI 18.0-57.5%]). When the period from the onset to isolation of the first household case was within 3 days, the secondary attack rate was low (4.5% [95% CI 0.1-22.8%]). Among the 21 secondary cases, 11 (52.4%) developed within 5 days of symptom onset in the first case within the same household. This indicates that secondary infection within the household occurred immediately after symptom onset in the first case. Therefore, isolation of a suspected patient can help reduce secondary household infections.

Seroepidemiological study of severe fever with thrombocytopenia syndrome in animals and humans in Okinawa, Japan.

In Okinawa prefecture, Japan, the first case of severe fever with thrombocytopenia syndrome (SFTS) was confirmed in August 2016, and this case remains to be the only reported case of SFTS in Okinawa. The epidemiological investigation indicated that the patient had been infected on the main island of Okinawa, but source and route of infection were unknown. Therefore, to understand the possible source and route of SFTS virus (SFTSV) infection in Okinawa, we performed a seroepidemiological study of SFTSV among animals and dwellers in Okinawa and conducted a questionnaire survey to investigate risk factors for tick bites in Okinawa. Among the 1,035 serum samples from four different animal species, anti-SFTSV antibodies were detected in only 4.2% wild mongoose (Herpestes auropunctatus) serum samples. To our knowledge, this is the first study to report the detection of anti-SFTSV antibodies in wild mongooses. Meanwhile, all 1,104 human inhabitants tested negative for anti-SFTSV antibodies, suggesting that the frequency of SFTSV exposure is low in Okinawa. Logistic regression analysis of the questionnaire results showed that outdoor activity was associated with an increased risk of tick bite among Okinawa residents. Despite the current low frequency of SFTSV infection in animals and humans, endemic circulation of the virus in Okinawa should be carefully monitored in the area for preventing future infections.

Molecular epidemiology of human metapneumovirus from 2009 to 2011 in Okinawa, Japan.

To clarify the molecular epidemiology of human metapneumovirus (HMPV) in Okinawa Prefecture, located in a subtropical region of Japan, we performed genetic analysis of the F gene in HMPV from patients with acute respiratory infection from January 2009 to December 2011. HMPV was detected in 18 of 485 throat swabs (3.7%). Phylogenetic analysis showed that 17 strains belonged to subgroup A2 and 1 strain belonged to subgroup B1. We did not observe seasonal prevalence of HMPV during the investigation period. A high level of sequence identity was observed in the strains belonging to subgroup A2 (>95%), and no amino acid substitution was found compared with other strains detected in Japan and other countries. The pairwise distance values among the present strains belonging to subgroup A2 were short. Our results suggest that the predominant HMPV strains belonging to A2 are highly homologous and seasonal epidemics were not seen in Okinawa during the investigation period.