An Outbreak of Human Parvovirus B19 Hidden by Dengue Fever.

BACKGROUND: Seasonal outbreaks of dengue often result in hundreds of dengue-suspected cases where a clinical diagnosis cannot be confirmed. Usually, during large outbreaks of dengue and other pathogens that can cause acute febrile illnesses, the search for secondary pathogens with similar disease outcomes is rare. METHODS: Using total RNA sequencing and targeted diagnostic assays, we discovered an outbreak of parvovirus B19 in dengue-suspected patients that occurred from November 2013 to February 2014. RESULTS: Of the 182 cases investigated, 63% were viremic for the B19 virus. Moreover, we found that >43% of infected patients had no serological evidence of prior infection. Parvovirus B19 is a typical childhood infection, yet we observed that 82% of the infected patients were adults. Additionally, we perceived that infected adults had significantly higher presentations of myalgia than in children. We also obtained viral protein (VP) 1/VP2 gene nucleotide sequences from 43 patients. CONCLUSIONS: Our results support the utility of next-generation sequencing for symptomatic patients with unknown etiologies during seasonal outbreaks of dengue and other arborviruses. Our findings could improve the vigilance of hospitals and laboratories by raising awareness of co-circulating pathogens such as parvovirus B19 that may be hidden in plain sight.

Epidemiological dynamics of an urban Dengue 4 outbreak in São Paulo, Brazil.

BACKGROUND: Dengue studies at the urban scale are scarce and required for guiding control efforts. In Brazil, the burden of dengue is high and challenges city public health administrations with limited resources. Here we studied the dynamics of a dengue epidemic in a single city. METHODS: Serum samples from dengue suspected cases were collected and tested, from December 2012 and July 2013 in Guarujá, Brazil. We use incidence series analysis to provide a detailed view of the reproduction number dynamics and a Bayesian analysis to infer the spread of the serotype using geographic and temporal data. RESULTS: We obtained nucleotide sequences from 354 envelope genes and georeferenced 286 samples during the course of the outbreak. Serotype 4 was responsible for the epidemic. We identified at least two major lineages that overlapped in distribution. We observed high reproduction numbers and high cladogenesis prior to the escalation of clinical case notifications. Three densely populated non-adjacent neighborhoods played a pivotal role during the onset and/or course of the epidemic. DISCUSSION: Our findings point to high dengue virus transmission with a substantial proportion of unapparent cases that led to a late recognition of an outbreak. Usually source reductions initiatives tend to be insufficient once an epidemic has been established. Nevertheless, health authorities in Guarujá prioritized vector control on specific places with clusters of georeferenced viremic patients, which appear to have diminished the epidemic impact.