The Reality of Outbreak Investigations: Dengue in Angola
July 18th, 2013 1:01 pm ET - Blog Administrator
By Tyler Sharp and Ryan R. HemmeMyth #1 Mystery Disease X
Although Hollywood likes to make it seem like every outbreak is a complete mystery, most of the time when a team goes into the field, preliminary diagnostic testing has already suggested the cause of the outbreak before a foot hits the ground. Nonetheless, whether the cause be viral, bacterial, parasitic, poison or toxin, a critical first step in every outbreak investigation is confirming the cause of the outbreak.It was no exception when we were sent to Angola to assist the Ministry of Health respond to a recently identified dengue outbreak in May of 2013. Dengue is an acute febrile illness that can cause explosive outbreaks. Although most people that get dengue will only suffer fever, headache, body pain, and possibly minor bleeding from the nose or gums, a relatively small proportion of people will develop severe dengue, which can result in hemorrhage, shock, and even death. By the time we were contacted, there were already dozens of sick people that had tested positive with a dengue rapid diagnostic test. Specimens were sent to CDC and the outbreak was confirmed soon after.
Myth # 2 Rushing into the field on a moment’s notice
The special red phone in the CDC Director’s office rings, an ominous look draws over their face, and a team is on a plane that evening, right? Not quite. There is a lot of careful planning that has to go into an outbreak response that may last weeks or longer in a country you’ve probably never visited. You have a limited idea of what exactly you’ll be doing once you get there, so you don’t immediately know what equipment and supplies will be needed in the field. In addition, most countries require visas to get in, which can take days or weeks to receive, even in an emergency. Finally, you have to coordinate with the host country to define an appropriate response. What CDC recommends may not be possible for many reasons, from the response being too ambitious to required resources not being available to lack of political support. Therefore, it’s important to pitch the plan to the local officials before arriving in the field. They may not come right out and say it, but hints of trepidation may mean that the plan needs to be revised. For that and many other reasons, flexibility is one of the most important traits that a “disease detective” can have. Before departing for Angola, we proposed to the local health authorities what we believed would be the most informative and feasible response to the ongoing epidemic, and then we tweaked the plan based on the feedback we received from them.
Priority #1 for the Angola dengue response was to raise awareness of the outbreak in the medical community. During dengue epidemics that occur in large, densely-populated cities like Luanda, the capital city of Angola, typically 5–10% of residents will become infected, so it’s not uncommon for hospital emergency rooms to become overrun with patients complaining of fever and body pain. Although there is no specific medication to cure dengue, early initiation of supportive therapy and close clinical monitoring can reduce the case-fatality rate for severe dengue from ~10% to < 0.1%. Therefore, clinicians need to know that a dengue epidemic is occurring, the criteria they should use to determine which patients can go home and which need to be hospitalized, and how best to care for those that are hospitalized. The first week that we arrived, Tyler worked with the Ministry of Health to train > 150 clinicians in two days, most of whom were sent home with training materials to train their colleagues.
Meanwhile, Ryan worked with staff from the Ministry of Health’s entomology and vector control programs. The Ministry has an established mosquito control program that is operated by very capable staff; however, in Angola the main concern is malaria, which is caused by a different mosquito than the one that transmits dengue, and the two mosquitoes behave quite differently. There are > 3,500 species and subspecies of mosquitoes, and each one has a unique biology. Some mosquitoes like the dengue vector Aedes aegypti prefer to lay eggs in water-filled containers, while others will readily lay their eggs in water on the ground. As an entomologist you have to know where to look for the mosquito you are interested in. After another lesson in the importance of being flexible following some snafus with getting our checked baggage, which contained all of our response supplies, Ryan was finally able to work with local staff to provide training and identify surveillance methods to attempt to control the mosquitoes causing the outbreak.Myth # 3 One of the “disease detectives” always gets infected
Does being in the field put you at greater risk for being infected with whatever bug is causing the outbreak? Probably, but we’re sent into the field with a small pharmacy of pills, sprays and ointments to either prevent us from getting sick or to treat us when we do get sick. Moreover, depending on the cause of the outbreak and what we’ll be doing in the field, we may bring additional personal protective equipment with us to keep us from being infected. Despite being vigilant about wearing mosquito repellent, on our last day in Luanda Ryan got bit by ravenous mosquito. He swatted it dead, examined it to identify it as Aedes aegypti, gave me a worried look and said, “I’m done for.” (Spoiler alert: Thankfully, neither of us ended up getting dengue during this response.)Myth # 4 CDC saves the day
In the movies, CDC is usually portrayed as a public health SWAT team. They storm in, identify the source of the outbreak, institute harsh but necessary containment measures, and ultimately stop the outbreak. In reality, it rarely works that way. First, CDC is only ever involved in an outbreak response by formal invitation from the state or country in which the outbreak is occurring. Second, CDC never acts alone. In Angola, we worked on the outbreak response with local health officials, foreign governments, USAID, World Health Organization, and local non governmental organizations. CDC is a very competent agency, but we rely on collaboration with local and international partners for a successful response.
Myth # 5 Outbreaks can rapidly spread worldwide
OK, this one is actually pretty accurate. The ease and frequency of international travel has increased the likelihood of cases from any given outbreak being imported into other cities, especially if the outbreak happens in a large, international city like Luanda. Around the end of our second week in the field, a report
came online documenting dengue in travelers to Luanda that were diagnosed after returning to their home countries on four different continents. Because of the oil industry, Luanda receives numerous international visitors each year, and some of them were bringing the unwanted souvenir of dengue back home with them. When physicians see a patient with a fever who has recently traveled to Africa, they are likely to suspect malaria, but not dengue. There were also three other dengue outbreaks in Africa in 2013, so the issue of clinical recognition of dengue was not likely to be limited to travelers returning from Angola. Because of this and the rapidly increasing case count, we decided to release an MMWR to notify clinicians in the U.S. and abroad of the need to be vigilant for dengue as a potential cause of fever in residents of and 
travelers returning from Angola. One of our important findings from the investigation was that genetic analysis of the virus revealed that it had been circulating in this region of Africa for the past 45 years. This meant that this was not a “new” outbreak of dengue, but rather that dengue was actually endemic in Angola and just hadn’t been recognized. These findings were in agreement with to a recent study suggesting that 64 million dengue virus infections occur each year in Africa.All in all, this investigation was an excellent example of the international team pulling together to get the job done quickly and correctly, and brought attention to a neglected tropical disease of significant public health importance. It was also a lesson to us that, unfortunately, reality isn’t always what Hollywood would have us believe.
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