The first Zika cases related to the current outbreak were found in Brazil in May 2015, along with a dramatic increase in microcephaly in babies born in that year. (See our previous blog about the possible link – now verified – between Zika and microcephaly.) Microcephaly is a serious birth defect that impacts many children whose mothers contract Zika while pregnant.
Active Zika transmission currently exists in nearly all of South and Central America, the Caribbean, and some Pacific Islands. 934 people in the US have been infected with Zika; 287 of those infected are pregnant women. Most of these people were infected outside the country and then traveled to the US. Zika is primarily spread by mosquitos, but can also be transmitted through blood transfusion, laboratory exposure and sexual contact.
While no cases of transmission by mosquito have yet been reported in the continental US, the Centers for Disease Control and Prevention (CDC) has released a blueprint for states to respond to locally transmitted cases of Zika. A visual diagram outlining the steps to be taken from the blueprint (a Process Map) can be helpful. (To view the Process Map for the CDC’s interim Zika response process, click on “Download PDF”.)
The CDC’s plan involves four stages. The first stage is implemented during mosquito season. This stage involves surveillance for suspected locally transmitted infections (i.e. persons with “symptoms compatible with Zika virus infection who do not have risk factors for acquisition through travel or sexual contact”, with pending test results). Upon a suspected infection, state officials and the CDC should be notified. State or local officials will open an epidemiological investigation (including ongoing surveillance) and begin implementing controls, involving both reducing mosquito populations and continuing public outreach, with CDC assistance as needed.
Stage 2 occurs upon confirmation of a locally transmitted infection. At this point, notification expands to include local blood centers as well as others required by International Health Regulations. The CDC will assist with an expanded investigation, surveillance, and communication, including deployment of an emergency response team (CERT) if desired. Once Stage 2 has been reached, stand down will only occur after 45 days (3 mosquito incubation periods) without additional infections or when environmental conditions no longer permit transmission.
If there is confirmed Zika in two or more persons whose movement during the exposure period overlaps within a one-mile diameter, Stage 3 (widespread local transmission) is entered. First, local officials will attempt to determine the transmission area, the “geographic area in which multiperson local transmission has occurred and may be ongoing”. Communication, surveillance, testing and controls are enhanced and expanded. Interventions for blood safety and vulnerable populations (including pregnant women) are implemented.
Once the infection has spread outside a county, it enters Stage 4 (widespread multijurisdictional transmission). All steps taken in previous stages are expanded and enhanced. The CDC will evaluate whether local capacity is adequate for response, and will assist as needed. Stage 4 actions will be continued until the criteria for stand down is met.
Based on previous experience with two mosquito-transmitted diseases, chikungunya & dengue fever, the CDC does not believe Stage 4 will be reached within the United States. However, as Dr. Tim F. Jones, an epidemiologist for the State of Tennessee, says, “Even though the percentages and the likelihoods are incredibly low, the outcome is awful.” Risk is a function of probability and consequence. Even with a low probability, the high consequence makes the risk from Zika considerable, and worth planning for.
To view the Process Map, click on “Download PDF” above. Or, click here to view the CDC’s interim guidance.