In November 2009, Saudi military forces previously stationed in other parts of the country were deployed to Jazan Province. This situation enabled us to look at baseline arbovirus seroprevalence in a group of new arrivals, stratified by province of origin. During May 8–12, 2010, we enrolled 1,026 soldiers in 5 Jazan administrative units near the border with Yemen in a study to evaluate serologic reactivity to AHFV, CCHFV, DENV, and RVFV. After receiving consent and assigning numeric identifiers to anonymize data, we used questionnaires to record Jazan arrival dates, home province, previous administrative residence, health histories, vector exposures, and other risk factors. Answers were reviewed onsite, and a 5-mL blood sample was collected. Serum samples from each soldier were labeled, archived, frozen, stored at –80°C, and transferred to the Ministry of Health central laboratory in Riyadh for testing. Questionnaire and testing data were entered in Epi Info software (wwwn.cdc.gov/epiinfo
) and then transferred to SPSS version 19.0 (IBM, Somers, NY, USA) for analysis.
A total of 197 (19%) enrolled soldiers reported symptomatic illness during deployment, 49 (25%) of whom were hospitalized. Reported signs and symptoms were fever (n = 81), rash (n = 50), and musculoskeletal complaints (n = 128). A diagnosis of malaria was recorded for 27 febrile soldiers and dengue fever for 1. Illnesses of the remaining soldiers were undiagnosed. As expected given the number of malaria cases, reported arthropod exposures favored mosquitoes over ticks, with 875 (85%) soldiers reporting mosquito contact compared with 153 (15%) reporting tick encounters. Thirty-seven (3%) soldiers reported contact with livestock carcasses, blood, or body fluids.
Serologic testing was completed for 1,024 soldiers; initial screening by IgG to each of the 4 viruses was followed by IgM testing of all IgG-reactive samples. Dengue antibodies were tested by using PanBio ELISA IgG (E-DEN02G; Inverness Medical Innovations, Sinnamon Park, QLD, Australia) and IgM (E-DEN01M; Inverness Medical Innovations) following manufacturer recommendations and protocols. IgG and IgM testing for AHFV, CCHV, and RVFV was done with Centers for Disease Control and Prevention (Atlanta, GA, USA) reagents and protocols by using cell culture–derived antigens (7,10,11
). Briefly, the ELISA antigens used to coat plates (for IgG) or detect captured IgM were produced by infecting Vero E6 cells with respective reference virus strains or by using uninfected cells for control. Each sample was tested at 4 dilutions (100, 400, 1,600, and 6,400). IgG reactivity/IgM nonreactivity was considered evidence of past infection; concurrent IgG/IgM reactivity was interpreted as infection within the previous 6 months. IgG-seropositive persons without histories of illness were considered to have had subclinical or very mild infection.
Forty reactive serum samples were identified, for a combined seroprevalence of 3.9 cases/100 soldiers tested: RVF (n = 20), AHFV (n = 13
), CCHV (n = 6
), and DENV (n = 1
) (). One soldier who had a positive test result for IgG and IgM to RVFV had a rash but no history of fever. No soldiers with AHFV, CCHFV, or DENV IgM were identified. We did not observe cross-reactivity of antibodies often seen with flaviviruses, and no person had positive test results against >1 antigen.
Serologic status of 1,024 soldiers evaluated for IgG and IgM ELISA reactivity against AHFV, CCHF, DENV, and RVFV antigens, Saudi Arabia, 2009*
Analysis of the province of origin provided AHFV epidemiologic information (). Two hundred sixty-eight (26%) soldiers were transferred to Jazan from Tabouk. This northern district accounted for most seropositive soldiers (8/13), 6 of whom might have resided in or visited a previously known AHFV-endemic region before transfer. Three AHFV-seropositive soldiers arrived from the Eastern Region; none had a previous residence or travel history elsewhere. In contrast, most RVFV-seropositive soldiers (18/20) and all 6 CCHV-seropositive soldiers had previously worked and resided in Jazan or other previously affected region. The only RVFV IgM-seropositive soldier listed a home residence and previous workplace in an AHFV-endemic region.
Figure Numbers of soldiers with seropositive test results distributed according to Saudi Arabian province before transfer to Jazan, 2009. Blue (n = 13), seropositive for Alkhurma hemorrhagic fever virus; red (n = 20), seropositive for Rift Valley fever virus. (more ...)