Epidemiological analysis of the Kaohsiung city strategy for dengue fever quarantine and epidemic prevention.

BACKGROUND: Dengue is endemic in over 100 countries and is an important public health problem worldwide. Dengue fever is not endemic in Taiwan; the importation of dengue viruses from neighboring countries via close commercial links and air travel is considered to be the cause of local outbreaks. Therefore, efforts toward disease control have focused on preventing the importation of dengue into Taiwan. In this study, we investigated the relationships between the numbers of imported and indigenous dengue cases to test the validity of this strategy. METHODS: Data on cases of dengue fever that occurred between 2013 and 2018 were obtained from the surveillance systems of the Taiwan Center for Disease Control and Kaohsiung City Health Department. Standard epidemiological data, including the monthly numbers of indigenous and imported cases of dengue, were calculated. Potential associations between the numbers of indigenous and imported cases were investigated using correlation analyses. RESULTS: We identified a possible relationship between the period of disease concealment and the number of imported dengue cases, which resulted in epidemics of indigenous dengue fever within local communities. Further analysis of confirmed cases during previous epidemics in Kaohsiung City found that the risk of indigenous dengue fever may be related to the likelihood that patients with imported dengue fever will stay within local communities. CONCLUSION: Given the correlations found between imported and indigenous cases of dengue fever, as well as the relationship between the disease concealment period and the risk of indigenous dengue fever, prevention of disease importation and efficient identification of dengue cases within high-risk communities remain the major priorities for disease control.

Cascading effect of economic globalization on human risks of scrub typhus and tick-borne rickettsial diseases.

The increase in global travel and trade has facilitated the dissemination of disease vectors. Globalization can also indirectly affect vector-borne diseases through the liberalization of cross-border trade, which has far-reaching, worldwide effects on agricultural practices and may in turn influence vectors through the modification of the ecological landscape. While the cascading effect of economic globalization on vector-borne diseases, sometimes acting synergistically with regional agricultural policy, could be substantial and have significant economic, agricultural, and public health implications, research into this remains very limited. We evaluated how abandonment of rice paddies in Taiwan after joining the World Trade Organization, along with periodic plowing, an agricultural policy to reduce farm pests in abandoned fields can unexpectedly influence risks to diseases transmitted by ticks and chiggers (larval trombiculid mites), which we collected from their small-mammal hosts. Sampling was limited to abandoned (fallow) and plowed fields due to the challenge of trapping small mammals in flooded rice paddies. Striped field mice (Apodemus agrarius) are the main hosts for both vectors. They harbored six times more ticks and three times more chiggers in fallow than in plowed plots. The proportion of ticks infected with Rickettsia spp. (etiologic agent of spotted fever) was three times higher in fallow plots, while that of Orientia tsutsugamushi (scrub typhus) in chiggers was similar in both treatments. Fallow plots had more ground cover and higher vegetation than plowed ones. Moreover, ticks and chiggers in both field types were dominated by species known to infest humans. Because ticks and chiggers should exhibit very low survival in flooded rice paddies, we propose that farm abandonment in Taiwan, driven by globalization, may have inadvertently led to increased risks of spotted fever and scrub typhus. However, periodic plowing can unintentionally mitigate vector burdens. Economic globalization can have unexpected consequences on disease risk through modification of the agricultural landscape, but the outcome may also be influenced by agricultural policies, calling for further research on vector-borne diseases and their control from broader perspectives.

Serologic assessment of the risk of developing chronic Q fever in cohorts of acutely infected individuals.

OBJECTIVE: The aim of this study was to assess the clinical significance of serological profiles suggestive of chronic Q fever after acute infection. METHODS: A prospective follow-up study consisting of two separate cohorts was conducted to monitor the serological evolution of Q fever. The first cohort comprised subjects with acute Q fever diagnosed in 2004-2007 and the second enrolled subjects whose infection occurred in 2009. The indirect immunofluorescence assay was used for serological monitoring, with serum PCR testing added for subjects whose serological profiles revealed high titers of anti-phase I IgG≥800, titers suggestive of chronic Q fever. RESULTS: In the first cohort of 92 persons, seventeen (18%) subjects had serological profiles suggestive of chronic Q fever (titers of anti-phase I IgG: 1280-5120, median: 1280) after a median follow-up period of 606.5 days. After a further follow-up (median period: 592 days) exclusively for those seventeen subjects, serological resolution with fourfold decrease of titers of anti-phase I IgG was noted in five of them. In the second cohort, only one (4%) of the twenty-eight subjects had high levels of anti-phase I IgG 180 days after acute infection. All the eighteen subjects with high levels of anti-phase I IgG were asymptomatic and had negative serum PCR testing. The different prevalence of subjects with high titers of anti-phase I IgG in the two cohorts was associated with duration of follow-up period (P < .01). CONCLUSIONS: Subjects with high titers of anti-phase I IgG≥800 was not uncommon and might not be detected until more than six months after acute Q fever infection. Asymptomatic subjects with high levels of anti-phase I IgG alone should not be treated as chronic Q fever and might not need continued serological monitoring in the absence of predisposing factors to chronic Q fever.