BACKGROUND: Chikungunya virus (ChikV) was introduced into the Caribbean in late 2013. In May, 2014, the Puerto Rico Department of Health (PRDOH) identified the first autochthonous case of chikungunya in a resident from the San Juan metro area. Despite anticipating the emergence of the virus in Puerto Rico (PR), surveillance for ChikV had not been implemented at that time. Clinical identification of ChikV can be challenging in PR with three additional acute febrile illnesses (AFIs) commonly identified: dengue, leptospirosis and influenza; Locally acquired Zika virus was also recently identified in PR. As chikungunya spread throughout PR, PRDOH and CDC collaborated to develop ChikV surveillance and provide epidemiological situational awareness to decision makers and clinicians.
METHODS: The Puerto Rico Department of Health, in conjunction with the CDC Dengue Branch, implemented a passive chikungunya surveillance system (PCSS) based on a passive dengue surveillance system (PDSS) in existence since the 1960s. Additionally, a pilot sentinel system was created among clinics and hospitals distributed throughout PR to collect specific symptomatology on patients identified as suspect cases by providers. Initially, PRDOH required submission of specimens for confirmatory testing and provider reporting of patients with clinically compatible illness (fever ≥ 38° C, arthralgia, and/or arthritis). As the epidemic progressed, under the strain of limited laboratory resources, testing protocols were changed to only include submission of specimens of hospitalized and high risk patients and continued reporting of chikungunya compatible cases.
RESULTS: During 2014 and 2015, 29,527 suspect cases (8.5 per 1,000 residents) were reported to the passive chikungunya surveillance system (PCSS). Of the 29,527 suspect cases, 4,539 cases were laboratory confirmed by PCR (>99%) or IgM. Of the 29,527 suspect cases, 31% or 9,151 underwent diagnostic testing.
CONCLUSIONS: Changes in reporting requirements and laboratory specimen submission protocols likely resulted in an inability to fully characterize the progression of the virus and provide an accurate estimate of the number of affected persons. The delay in the implementation of a chikungunya surveillance system put unnecessary strain on an already resource limited public health system. Designing and implementing an effective chikungunya surveillance system in the presence of other AFIs with overlapping signs and symptoms continues to challenge public health in PR. Improvements in laboratory capacity such as AFI panel testing and improved clinician outreach for proper case identification would likely allow for improved ChikV epidemiology and improved characterization of this and other AFIs in Puerto Rico.