Clinical Characteristics, Histopathology, and Tissue Immunolocalization of Chikungunya Virus Antigen in Fatal Cases.

BACKGROUND: Death in patients with chikungunya is rare and has been associated with encephalitis, hemorrhage, and septic shock. We describe clinical, histologic, and immunohistochemical findings in individuals who died following chikungunya virus (CHIKV) infection. METHODS: We identified individuals who died in Puerto Rico during 2014 following an acute illness and had CHIKV RNA detected by reverse transcriptase-polymerase chain reaction in a pre- or postmortem blood or tissue specimen. We performed histopathology and immunohistochemistry (IHC) for CHIKV antigen on tissue specimens and collected medical data via record review and family interviews. RESULTS: Thirty CHIKV-infected fatal cases were identified (0.8/100 000 population). The median age was 61 years (range: 6 days-86 years), and 19 (63%) were male. Death occurred a median of 4 days (range: 1-29) after illness onset. Nearly all (93%) had at least 1 comorbidity, most frequently hypertension, diabetes, or obesity. Nine had severe comorbidities (eg, chronic heart or kidney disease, sickle cell anemia) or coinfection (eg, leptospirosis). Among 24 fatal cases with tissue specimens, 11 (46%) were positive by IHC. CHIKV antigen was most frequently detected in mesenchymal tissues and mononuclear cells including tissue macrophages, blood mononuclear cells, splenic follicular dendritic cells, and Kupffer cells. Common histopathologic findings were intra-alveolar hemorrhage and edema in the lung, chronic or acute tenosynovitis, and increased immunoblasts in the spleen. CHIKV infection likely caused fatal septic shock in 2 patients. CONCLUSIONS: Evaluation of tissue specimens provided insights into the pathogenesis of CHIKV, which may rarely result in septic shock and other severe manifestations.

Evaluating Differences in Whole Blood, Serum, and Urine Screening Tests for Zika Virus, Puerto Rico, USA, 2016.

We evaluated nucleic acid amplification testing (NAAT) for Zika virus on whole-blood specimens compared with NAAT on serum and urine specimens among asymptomatic pregnant women during the 2015-2016 Puerto Rico Zika outbreak. Using NAAT, more infections were detected in serum and urine than in whole blood specimens.

Characterizing environmental asthma triggers and healthcare use patterns in Puerto Rico.

Objective: Asthma carries a high burden of disease for residents of Puerto Rico. We conducted this study to better understand asthma-related healthcare use and to examine potential asthma triggers.Methods: We characterized asthma-related healthcare use in 2013 by demographics, region, and date using outpatient, hospital, and emergency department (ED) insurance claims with a primary diagnostic ICD-9-CM code of 493.XX. We examined environmental asthma triggers, including outdoor allergens (i.e., mold and pollen), particulate pollution, and influenza-like illness. Analyses included descriptive statistics and Poisson time-series regression.Results: During 2013, there were 550,655 medical asthma claims reported to the Puerto Rico Healthcare Utilization database, representing 148 asthma claims/1,000 persons; 71% of asthma claims were outpatient visits, 19% were hospitalizations, and 10% were ED visits. Females (63%), children aged ≤9 years (77% among children), and adults aged ≥45 years (80% among adults) had the majority of asthma claims. Among health regions, Caguas had the highest asthma claim-rate at 142/1,000 persons (overall health region claim-rate = 108). Environmental exposures varied across the year and demonstrated seasonal patterns. Metro health region regression models showed positive associations between increases in mold and particulate matter <10 microns in diameter (PM10) and outpatient asthma claims.Conclusions: This study provides information about patterns of asthma-related healthcare use across Puerto Rico. Increases in mold and PM10 were associated with increases in asthma claims. Targeting educational interventions on exposure awareness and reduction techniques, especially to persons with higher asthma-related healthcare use, can support asthma control activities in public health and clinical settings.

Community Understanding of Contraception During the Zika Virus Outbreak in Puerto Rico.

In response to the Zika virus outbreak in Puerto Rico (2015-2016), the Zika Contraception Access Network (Z-CAN) was established to provide same-day access to the full range of reversible contraception at no cost to women. Formative research was conducted to inform the development of a communication campaign about Z-CAN. Ten focus groups with women and men, aged 18 to 49 years, in Puerto Rico were conducted to collect data on contraception awareness, use, and decision making during the Zika outbreak, as well as culturally appropriate messaging and outreach strategies. Thematic analysis was conducted using the constant comparative method. Data showed that there was community awareness regarding Zika in Puerto Rico. However, it was not a motivating factor in contraception decision making; instead, economic factors were the major drivers. Most participants preferred to receive information on contraception, potential side effects, and where to access contraceptive services via Internet-based channels and health care providers. Based on these findings, the Ante La Duda, Pregunta [When in Doubt, Ask] campaign was launched to promote awareness of Z-CAN services among those who chose to prevent pregnancy during the Zika outbreak. Our results underscore the importance of conducting formative research to develop communication initiatives, while also demonstrating that it is feasible to perform these activities as part of an emergency response.

Seroprevalence, Risk Factors, and Rodent Reservoirs of Leptospirosis in an Urban Community of Puerto Rico, 2015.

BACKGROUND: The burden of leptospirosis in Puerto Rico remains unclear due to underreporting. METHODS: A cross-sectional survey and rodent trapping was performed in a community within San Juan, Puerto Rico to determine the seroprevalence and risk factors for Leptospira infection. The microscopic agglutination test was used to detect anti-Leptospira antibodies as a marker of previous infection. We evaluated Leptospira carriage by quantitative polymerase chain reaction among rodents trapped at the community site. RESULTS: Of 202 study participants, 55 (27.2%) had Leptospira agglutinating antibodies. Among the 55 seropositive individuals, antibodies were directed most frequently against serogroups Icterohaemorrhagiae (22.0%) and Autumnalis (10.6%). Of 18 captured rodents, 11 (61.1%) carried pathogenic Leptospira (Leptospira borgpetersenii, 7 and Leptospira interrogans, 2). Four participants showed their highest titer against an isolate obtained from a rodent (serogroup Ballum). Increasing household distance to the canal that runs through the community was associated with decreased risk of infection (odds ratio = 0.934 per 10-meter increase; 95% confidence interval, .952-.992). CONCLUSIONS: There are high levels of Leptospira exposure in an urban setting in Puerto Rico, for which rodents may be an important reservoir for transmission. Our findings indicate that prevention should focus on mitigating risk posed by infrastructure deficiencies such as the canal.

Differences in Prevalence of Symptomatic Zika Virus Infection, by Age and Sex-Puerto Rico, 2016.

Background: During the outbreak of Zika virus (ZIKV) disease in Puerto Rico in 2016, nonpregnant women aged 20-39 years were disproportionately identified with ZIKV disease. We used household-based cluster investigations to determine whether this disparity was associated with age- or sex-dependent differences in the rate of ZIKV infection or reported symptoms. Methods: Participation was offered to residents of households within a 100-m radius of the residences of a convenience sample of 19 laboratory-confirmed ZIKV disease cases. Participants answered a questionnaire and provided specimens for diagnostic testing by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Results: Among 367 study participants, 114 (31.1%) were laboratory positive for ZIKV infection, of whom 30% reported a recent illness (defined as self-reported rash or arthralgia) attributable to ZIKV infection. Age and sex were not associated with ZIKV infection. Female sex (adjusted prevalence ratio [aPR], 2.28; 95% confidence interval [CI], 1.40, 3.67), age <40 years (aPR, 2.39; 95% CI, 1.55, 3.70), and asthma (aPR, 1.63; 95% CI, 1.12, 2.37) were independently associated with symptomatic infection. Conclusions: Although neither female sex nor age were associated with an increased prevalence of ZIKV infection, both were associated with symptomatic infection. Further investigation to identify a potential mechanism of age- and sex-dependent differences in reporting symptomatic ZIKV infection is warranted.

Implementation and Evaluation of Guillain-Barré Syndrome Surveillance in Puerto Rico during the 2016 Zika Virus Epidemic.

OBJECTIVE: Guillain-Barré syndrome (GBS) is an uncommon autoimmune disorder that follows infection or vaccination, and increased incidence has been reported during Zika virus (ZIKV) transmission. During the 2016 ZIKV epidemic, the Puerto Rico Department of Health (PRDH) implemented the Enhanced GBS Surveillance System (EGBSSS). Here, we describe EGBSSS implementation and evaluate completeness, validity, and timeliness. METHODS: GBS cases were identified using passive surveillance and discharge diagnostic code for GBS. Completeness was evaluated by capture-recapture methods. Sensitivity and positive predictive value (PPV) for confirmed GBS cases were calculated for both case identification methods. Median time to completion of key time steps were compared by quarter (Q1-4) and hospital size. RESULTS: A total of 122 confirmed GBS cases with onset of neurologic illness in 2016 were identified. Capture-recapture methodology estimated that four confirmed GBS cases were missed by both identification methods. Identification of cases by diagnostic code had a higher sensitivity than passive surveillance (89% vs. 80%), but a lower PPV (60% vs. 72%). There was a significant decrease from Q1 to Q3 in median time from hospital admission to case reporting (11 days vs. 2 days, p = 0.032) and from Q2 to Q3 in median time from specimen receipt to arbovirus laboratory test reporting (35 days vs. 26 days, p = 0.004). CONCLUSION: EGBSSS provided complete, valid, and increasingly timely surveillance data, which guided public health action and supported healthcare providers during the ZIKV epidemic. This evaluation provides programmatic lessons for GBS surveillance and emergency response surveillance.

Guillain-Barré Syndrome and Healthcare Needs during Zika Virus Transmission, Puerto Rico, 2016.

To assist with public health preparedness activities, we estimated the number of expected cases of Zika virus in Puerto Rico and associated healthcare needs. Estimated annual incidence is 3.2-5.1 times the baseline, and long-term care needs are predicted to be 3-5 times greater than in years with no Zika virus.

Use of Blood Donor Screening Data to Estimate Zika Virus Incidence, Puerto Rico, April-August 2016.

Puerto Rico has been heavily impacted by Zika virus, a mosquitoborne flavivirus that emerged in the Americas during 2015. Although most persons with Zika virus show no symptoms, the virus can cause neurologic and other complications, including fetal microcephaly. Local Zika virus transmission in Puerto Rico has been reported since December 2015. To prevent transfusion-associated transmission, local blood collection ceased in March 2016 but resumed in April 2016 after Zika virus screening of blood donations became available. Using data from screening of blood donations collected by the 2 largest blood centers in Puerto Rico during April 3-August 12, 2016, and assuming a 9.9-day duration of viremia, we estimated that 469,321 persons in Puerto Rico were infected during this period, for an estimated cumulative incidence of 12.9%. Results from blood donation screening during arboviral outbreaks can supplement routine clinical and surveillance data for improved targeting of prevention efforts.

Cost-effectiveness of Increasing Access to Contraception during the Zika Virus Outbreak, Puerto Rico, 2016.

We modeled the potential cost-effectiveness of increasing access to contraception in Puerto Rico during a Zika virus outbreak. The intervention is projected to cost an additional $33.5 million in family planning services and is likely to be cost-saving for the healthcare system overall. It could reduce Zika virus-related costs by $65.2 million ($2.8 million from less Zika virus testing and monitoring and $62.3 million from avoided costs of Zika virus-associated microcephaly [ZAM]). The estimates are influenced by the contraception methods used, the frequency of ZAM, and the lifetime incremental cost of ZAM. Accounting for unwanted pregnancies that are prevented, irrespective of Zika virus infection, an additional $40.4 million in medical costs would be avoided through the intervention. Increasing contraceptive access for women who want to delay or avoid pregnancy in Puerto Rico during a Zika virus outbreak can substantially reduce the number of cases of ZAM and healthcare costs.

Surveillance for Chikungunya and Dengue During the First Year of Chikungunya Virus Circulation in Puerto Rico.

After chikungunya virus (CHIKV) transmission was detected in Puerto Rico in May 2014, multiple surveillance systems were used to describe epidemiologic trends and CHIKV-associated disease. Of 28 327 cases reported via passive surveillance, 6472 were tested for evidence of CHIKV infection, and results for 4399 (68%) were positive. Of 250 participants in household cluster investigations, 70 (28%) had evidence of recent CHIKV infection. Enhanced surveillance for chikungunya at 2 hospitals identified 1566 patients who tested positive for CHIKV, of whom 10.9% were hospitalized. Enhanced surveillance for fatal cases enabled identification of 31 cases in which CHIKV was detected in blood or tissue specimens. All surveillance systems detected a peak incidence of chikungunya in September 2014 and continued circulation in 2015. Concomitant surveillance for dengue demonstrated low incidence, which had decreased before CHIKV was introduced. Multifaceted chikungunya surveillance in Puerto Rico resolved gaps in traditional passive surveillance and enabled a holistic description of the spectrum of disease associated with CHIKV infection.

Zika Virus Infection Associated With Severe Thrombocytopenia.

We report two patients that developed severe thrombocytopenia after Zika virus (ZIKV) infection. The first patient had 1000 platelets/µL and died after multiple hemorrhages. The second patient had 2000 platelets/µL, had melena and ecchymoses, and recovered after receiving intravenous immunoglobulin. ZIKV may be associated with immune-mediated severe thrombocytopenia.

Survey of Blood Collection Centers and Implementation of Guidance for Prevention of Transfusion-Transmitted Zika Virus Infection--Puerto Rico, 2016.

Since November 2015, Puerto Rico has reported active mosquito-borne transmission of Zika virus. Because of the potential for Zika virus to be transmitted through transfusion of blood components, and because a high percentage of persons infected with Zika virus are asymptomatic, the Food and Drug Administration (FDA) recommended that blood collections cease in areas of the United States affected by active vector-borne transmission of Zika virus until laboratory screening of blood donations or pathogen reduction technology (PRT) for treatment of blood components can be implemented. To inform efforts to maintain the safety and availability of the blood supply in Puerto Rico, CDC, in collaboration with the Puerto Rico Department of Health, conducted a rapid assessment of blood collection and use on the island. A total of 139,369 allogeneic red blood cell (RBC) units, 45,243 platelet units, and 56,466 plasma units were collected in or imported to Puerto Rico during 2015, and 135,966 allogeneic RBC units, 13,526 therapeutic platelet units, and 25,775 plasma units were transfused. Because of the potential for local Zika virus transmission in areas with a competent mosquito vector, other areas of the United States should develop plans to ensure local blood safety and adequacy. Blood collection organizations and public health agencies should collaborate to maintain the safety and availability of local blood supplies in accordance with FDA guidance.

Incidence of Zika Virus Disease by Age and Sex - Puerto Rico, November 1, 2015-October 20, 2016.

Zika virus is a flavivirus transmitted primarily by Aedes species mosquitoes; symptoms of infection include rash, arthralgia, fever, and conjunctivitis.*,† Zika virus infection during pregnancy can cause microcephaly and other serious brain anomalies (1), and in rare cases, Zika virus infection has been associated with Guillain-Barré syndrome (2) and severe thrombocytopenia (3). This report describes the incidence of reported symptomatic Zika virus disease in the U.S. territory of Puerto Rico by age and sex. During November 1, 2015-October 20, 2016, 62,500 suspected Zika virus disease cases were reported to the Puerto Rico Department of Health (PRDH); 29,345 (47%) were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) testing, or were presumptively diagnosed based on serological testing. The highest incidence among confirmed or presumptive cases occurred among persons aged 20-29 years (1,150 cases per 100,000 residents). Among 28,219 (96.2%) nonpregnant patients with confirmed or presumptive Zika virus disease, incidence was higher among women (936 per 100,000 population) than men (576 per 100,000) for all age groups ≥20 years, and the majority (61%) of reported Zika virus disease cases occurred in females. Among suspected Zika virus disease cases in nonpregnant adults aged ≥40 years, the percentage that tested positive among females (52%) was higher than that among males (47%) (p<0.01). Reasons for the higher incidence of Zika virus disease among women aged ≥20 years are not known; serosurveys of persons living near confirmed Zika virus disease cases might help to elucidate these findings. Residents of and travelers to Puerto Rico should remove or cover standing water, practice mosquito abatement, employ mosquito bite avoidance behaviors, take precautions to reduce the risk for sexual transmission, and seek medical care for any acute illness with rash or fever.

Local Transmission of Zika Virus--Puerto Rico, November 23, 2015-January 28, 2016.

Zika virus, a mosquito-borne flavivirus, spread to the Region of the Americas (Americas) in mid-2015, and appears to be related to congenital microcephaly and Guillain-Barré syndrome (1,2). On February 1, 2016, the World Health Organization (WHO) declared the occurrence of microcephaly cases in association with Zika virus infection to be a Public Health Emergency of International Concern.* On December 31, 2015, Puerto Rico Department of Health (PRDH) reported the first locally acquired (index) case of Zika virus disease in a jurisdiction of the United States in a patient from southeastern Puerto Rico. During November 23, 2015-January 28, 2016, passive and enhanced surveillance for Zika virus disease identified 30 laboratory-confirmed cases. Most (93%) patients resided in eastern Puerto Rico or the San Juan metropolitan area. The most frequently reported signs and symptoms were rash (77%), myalgia (77%), arthralgia (73%), and fever (73%). Three (10%) patients were hospitalized. One case occurred in a patient hospitalized for Guillain-Barré syndrome, and one occurred in a pregnant woman. Because the most common mosquito vector of Zika virus, Aedes aegypti, is present throughout Puerto Rico, Zika virus is expected to continue to spread across the island. The public health response in Puerto Rico is being coordinated by PRDH with assistance from CDC. Clinicians in Puerto Rico should report all cases of microcephaly, Guillain-Barré syndrome, and suspected Zika virus disease to PRDH. Other adverse reproductive outcomes, including fetal demise associated with Zika virus infection, should be reported to PRDH. To avoid infection with Zika virus, residents of and visitors to Puerto Rico, particularly pregnant women, should strictly follow steps to avoid mosquito bites, including wearing pants and long-sleeved shirts, using permethrin-treated clothing and gear, using an Environmental Protection Agency (EPA)-registered insect repellent, and ensuring that windows and doors have intact screens.

Possible Zika Virus Infection Among Pregnant Women - United States and Territories, May 2016.

Zika virus is a cause of microcephaly and brain abnormalities (1), and it is the first known mosquito-borne infection to cause congenital anomalies in humans. The establishment of a comprehensive surveillance system to monitor pregnant women with Zika virus infection will provide data to further elucidate the full range of potential outcomes for fetuses and infants of mothers with asymptomatic and symptomatic Zika virus infection during pregnancy. In February 2016, Zika virus disease and congenital Zika virus infections became nationally notifiable conditions in the United States (2). Cases in pregnant women with laboratory evidence of Zika virus infection who have either 1) symptomatic infection or 2) asymptomatic infection with diagnosed complications of pregnancy can be reported as cases of Zika virus disease to ArboNET* (2), CDC's national arboviral diseases surveillance system. Under existing interim guidelines from the Council for State and Territorial Epidemiologists (CSTE), asymptomatic Zika virus infections in pregnant women who do not have known pregnancy complications are not reportable. ArboNET does not currently include pregnancy surveillance information (e.g., gestational age or pregnancy exposures) or pregnancy outcomes. To understand the full impact of infection on the fetus and neonate, other systems are needed for reporting and active monitoring of pregnant women with laboratory evidence of possible Zika virus infection during pregnancy. Thus, in collaboration with state, local, tribal, and territorial health departments, CDC established two surveillance systems to monitor pregnancies and congenital outcomes among women with laboratory evidence of Zika virus infection(†) in the United States and territories: 1) the U.S. Zika Pregnancy Registry (USZPR),(§) which monitors pregnant women residing in U.S. states and all U.S. territories except Puerto Rico, and 2) the Zika Active Pregnancy Surveillance System (ZAPSS), which monitors pregnant women residing in Puerto Rico. As of May 12, 2016, the surveillance systems were monitoring 157 and 122 pregnant women with laboratory evidence of possible Zika virus infection from participating U.S. states and territories, respectively. Tracking and monitoring clinical presentation of Zika virus infection, all prenatal testing, and adverse consequences of Zika virus infection during pregnancy are critical to better characterize the risk for congenital infection, the performance of prenatal diagnostic testing, and the spectrum of adverse congenital outcomes. These data will improve clinical guidance, inform counseling messages for pregnant women, and facilitate planning for clinical and public health services for affected families.

Screening of Blood Donations for Zika Virus Infection - Puerto Rico, April 3-June 11, 2016.

Transfusion-transmitted infections have been documented for several arboviruses, including West Nile and dengue viruses (1). Zika virus, a flavivirus transmitted primarily by Aedes aegypti mosquitoes that has been identified as a cause of congenital microcephaly and other serious brain defects (2), became recognized as a potential threat to blood safety after reports from a 2013-2014 outbreak in French Polynesia. Blood safety concerns were based on very high infection incidence in the population at large during epidemics, the high percentage of persons with asymptomatic infection, the high proportion of blood donations with evidence of Zika virus nucleic acid upon retrospective testing, and an estimated 7-10-day period of viremia (3). At least one instance of transfusion transmission of Zika virus has been documented in Brazil after the virus emerged there, likely in 2014 (4). Rapid epidemic spread has followed to other areas of the Americas, including Puerto Rico.

Guillain-Barré Syndrome During Ongoing Zika Virus Transmission - Puerto Rico, January 1-July 31, 2016.

Guillain-Barré syndrome (GBS) is a postinfectious autoimmune disorder characterized by bilateral flaccid limb weakness attributable to peripheral nerve damage (1). Increased GBS incidence has been reported in countries with local transmission of Zika virus, a flavivirus transmitted primarily by certain Aedes species mosquitoes (2). In Puerto Rico, three arthropod-borne viruses (arboviruses) are currently circulating: Zika, dengue, and chikungunya. The first locally acquired Zika virus infection in Puerto Rico was reported in December 2015 (3). In February 2016, the Puerto Rico Department of Health (PRDH), with assistance from CDC, implemented the GBS Passive Surveillance System (GBPSS) to identify new cases of suspected GBS (4). Fifty-six suspected cases of GBS with onset of neurologic signs during January 1-July 31, 2016, were identified. Thirty-four (61%) patients had evidence of Zika virus or flavivirus infection; the median age of these patients was 55 years (range = 21-88 years), and 20 (59%) patients were female. These 34 patients were residents of seven of eight PRDH public health regions. All 34 patients were hospitalized and treated with intravenous immunoglobulin G (IVIg), the standard treatment for GBS; 21 (62%) required intensive care unit admission, including 12 (35%) who required endotracheal intubation and mechanical ventilation. One patient died of septic shock after treatment for GBS. Additionally, 26 cases of neurologic conditions other than GBS were reported through GBPSS, including seven (27%) in patients with evidence of Zika virus or flavivirus infection. Residents of and travelers to Puerto Rico and countries with active Zika virus transmission should follow recommendations for prevention of Zika virus infections.* Persons with signs or symptoms consistent with GBS should promptly seek medical attention. Health care providers in areas with ongoing local transmission seeing patients with neurologic illnesses should consider GBS and report suspected cases to public health authorities.

Update: Ongoing Zika Virus Transmission - Puerto Rico, November 1, 2015-April 14, 2016.

Zika virus is a flavivirus transmitted primarily by Aedes species mosquitoes, and symptoms of infection can include rash, fever, arthralgia, and conjunctivitis (1).* Zika virus infection during pregnancy is a cause of microcephaly and other severe brain defects (2). Infection has also been associated with Guillain-Barré syndrome (3). In December 2015, Puerto Rico became the first U.S. jurisdiction to report local transmission of Zika virus, with the index patient reporting symptom onset on November 23, 2015 (4). This report provides an update to the epidemiology of and public health response to ongoing Zika virus transmission in Puerto Rico. During November 1, 2015-April 14, 2016, a total of 6,157 specimens from suspected Zika virus-infected patients were evaluated by the Puerto Rico Department of Health (PRDH) and CDC Dengue Branch (which is located in San Juan, Puerto Rico), and 683 (11%) had laboratory evidence of current or recent Zika virus infection by one or more tests: reverse transcription-polymerase chain reaction (RT-PCR) or immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA). Zika virus-infected patients resided in 50 (64%) of 78 municipalities in Puerto Rico. Median age was 34 years (range = 35 days-89 years). The most frequently reported signs and symptoms were rash (74%), myalgia (68%), headache (63%), fever (63%), and arthralgia (63%). There were 65 (10%) symptomatic pregnant women who tested positive by RT-PCR or IgM ELISA. A total of 17 (2%) patients required hospitalization, including 5 (1%) patients with suspected Guillain-Barré syndrome. One (<1%) patient died after developing severe thrombocytopenia. The public health response to the outbreak has included increased laboratory capacity to test for Zika virus infection (including blood donor screening), implementation of enhanced surveillance systems, and prevention activities focused on pregnant women. Vector control activities include indoor and outdoor residual spraying and reduction of mosquito breeding environments focused around pregnant women's homes. Residents of and travelers to Puerto Rico should continue to employ mosquito bite avoidance behaviors, take precautions to reduce the risk for sexual transmission (5), and seek medical care for any acute illness with rash or fever.

Update: Ongoing Zika Virus Transmission - Puerto Rico, November 1, 2015-July 7, 2016.

Zika virus is a flavivirus transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes, and infection can be asymptomatic or result in an acute febrile illness with rash (1). Zika virus infection during pregnancy is a cause of microcephaly and other severe birth defects (2). Infection has also been associated with Guillain-Barré syndrome (GBS) (3) and severe thrombocytopenia (4,5). In December 2015, the Puerto Rico Department of Health (PRDH) reported the first locally acquired case of Zika virus infection. This report provides an update to the epidemiology of and public health response to ongoing Zika virus transmission in Puerto Rico (6,7). A confirmed case of Zika virus infection is defined as a positive result for Zika virus testing by reverse transcription-polymerase chain reaction (RT-PCR) for Zika virus in a blood or urine specimen. A presumptive case is defined as a positive result by Zika virus immunoglobulin M (IgM) enzyme-linked immunosorbent assay (MAC-ELISA)* and a negative result by dengue virus IgM ELISA, or a positive test result by Zika IgM MAC-ELISA in a pregnant woman. An unspecified flavivirus case is defined as positive or equivocal results for both Zika and dengue virus by IgM ELISA. During November 1, 2015-July 7, 2016, a total of 23,487 persons were evaluated by PRDH and CDC Dengue Branch for Zika virus infection, including asymptomatic pregnant women and persons with signs or symptoms consistent with Zika virus disease or suspected GBS; 5,582 (24%) confirmed and presumptive Zika virus cases were identified. Persons with Zika virus infection were residents of 77 (99%) of Puerto Rico's 78 municipalities. During 2016, the percentage of positive Zika virus infection cases among symptomatic males and nonpregnant females who were tested increased from 14% in February to 64% in June. Among 9,343 pregnant women tested, 672 had confirmed or presumptive Zika virus infection, including 441 (66%) symptomatic women and 231 (34%) asymptomatic women. One patient died after developing severe thrombocytopenia (4). Evidence of Zika virus infection or recent unspecified flavivirus infection was detected in 21 patients with confirmed GBS. The widespread outbreak and accelerating increase in the number of cases in Puerto Rico warrants intensified vector control and personal protective behaviors to prevent new infections, particularly among pregnant women.