Publications

2019
Wound Botulism Outbreak Among People Who Use Black Tar Heroin ― San Diego County, California, 2017–2018
Peak CM, Rosen H, Kamali A, et al. Wound Botulism Outbreak Among People Who Use Black Tar Heroin ― San Diego County, California, 2017–2018. Morbidity and Mortality Weekly Report. 2019;67 (5152) :1415-1418. Publisher's Version
2018
Unresolved Splenomegaly in Recently Resettled Congolese Refugees ― Multiple States, 2015–2018.
Zambrano LD, Samson O, Phares C, et al. Unresolved Splenomegaly in Recently Resettled Congolese Refugees ― Multiple States, 2015–2018. Morbidity and Mortality Weekly Report. 2018;67 (49) :1358-1362. Publisher's VersionAbstract
In 2014, panel physicians from the International Organization for Migration (IOM), who conduct Department of State–required predeparture examinations for U.S.-bound refugees at resettlement sites in Uganda, noticed an unusually high number of Congolese refugees with enlarged spleens, or splenomegaly. Many conditions can cause splenomegaly, such as various infections, liver disease, and cancer. Splenomegaly can result in hematologic disturbances and abdominal pain and can increase the risk for splenic rupture from blunt trauma, resulting in life-threatening internal bleeding. On CDC’s advice, panel physicians implemented an enhanced surveillance and treatment protocol that included screening for malaria (through thick and thin smears and rapid diagnostic testing), schistosomiasis, and several other conditions; treatment of any condition identified as potentially associated with splenomegaly; and empiric treatment for the most likely etiologies, including malaria and schistosomiasis. CDC recommended further treatment for malaria with primaquine after arrival, after glucose-6-phosphate dehydrogenase testing, to target liver-stage parasites. Despite this recommended treatment protocol, 35 of 64 patients with available follow-up records had splenomegaly that persisted beyond 6 months after resettlement. Among 85 patients who were diagnosed with splenomegaly through abdominal palpation or ultrasound at any point after resettlement, 53 had some hematologic abnormality (leukopenia, anemia, or thrombocytopenia), 16 had evidence of current or recent malaria infection, and eight had evidence of schistosomiasis. Even though primaquine was provided to a minority of patients in this cohort, it should be provided to all eligible patients with persistent splenomegaly, and repeated antischistosomal therapy should be provided to patients with evidence of current or recent schistosomiasis. Given substantial evidence of familial clustering of cases, family members of patients with known splenomegaly should be proactively screened for this condition.
Population mobility reductions associated with travel restrictions during the Ebola epidemic in Sierra Leone: use of mobile phone data
Peak CM, Wesolowski A, zu Erbach-Schoenberg E, et al. Population mobility reductions associated with travel restrictions during the Ebola epidemic in Sierra Leone: use of mobile phone data. International Journal of Epidemiology. 2018. Publisher's VersionAbstract
Background: Travel restrictions were implementeded on an unprecedented scale in 2015 in Sierra Leone to contain and eliminate Ebola virus disease. However, the impact of epidemic travel restrictions on mobility itself remains difficult to measure with traditional methods. New ‘big data’ approaches using mobile phone data can provide, in near real-time, the type of information needed to guide and evaluate control measures.

Methods: We analysed anonymous mobile phone call detail records (CDRs) from a lead- ing operator in Sierra Leone between 20 March and 1 July in 2015. We used an anomaly detection algorithm to assess changes in travel during a national ‘stay at home’ lock- down from 27 to 29 March. To measure the magnitude of these changes and to assess effect modification by region and historical Ebola burden, we performed a time series analysis and a crossover analysis.

Results: Routinely collected mobile phone data revealed a dramatic reduction in human mobility during a 3-day lockdown in Sierra Leone. The number of individuals relocating between chiefdoms decreased by 31% within 15 km, by 46% for 15–30 km and by 76% for distances greater than 30 km. This effect was highly heterogeneous in space, with higher impact in regions with higher Ebola incidence. Travel quickly returned to normal patterns after the restrictions were lifted.

Conclusions: The effects of travel restrictions on mobility can be large, targeted and measurable in near real-time. With appropriate anonymization protocols, mobile phone data should play a central role in guiding and monitoring interventions for epidemic containment.

Prolonging herd immunity to cholera via vaccination: Accounting for human mobility and waning vaccine effects
Peak CM, Reilly AL, Azman AS, Buckee CO. Prolonging herd immunity to cholera via vaccination: Accounting for human mobility and waning vaccine effects. PLOS Neglected Tropical Diseases. 2018;12 (2) :e0006257. Publisher's Version
Productive disruption: opportunities and challenges for innovation in infectious disease surveillance
Buckee CO, Cardenas MIE, Corpuz J, et al. Productive disruption: opportunities and challenges for innovation in infectious disease surveillance. BMJ Global Health. 2018;3 (1). Publisher's Version
2017
Comparing nonpharmaceutical interventions for containing emerging epidemics
Peak CM, Childs LM, Grad YH, Buckee CO. Comparing nonpharmaceutical interventions for containing emerging epidemics. Proceedings of the National Academy of Sciences. 2017. Publisher's VersionAbstract

 

Quarantine and symptom monitoring of contacts with suspected exposure to an infectious disease are key interventions for the control of emerging epidemics; however, there does not yet exist a quantitative framework for comparing the control performance of each intervention. Here, we use a mathematical model of seven case-study diseases to show how the choice of intervention is influenced by the natural history of the infectious disease, its inherent transmissibility, and the intervention feasibility in the particular healthcare setting. We use this information to identify the most important characteristics of the disease and setting that need to be considered for an emerging pathogen to make an informed decision between quarantine and symptom monitoring.

 

2016
Fractional Dosing of Yellow Fever Vaccine to Extend Supply: A Modeling Study
WU JT, Peak CM, Leung GM, Lipsitch M. Fractional Dosing of Yellow Fever Vaccine to Extend Supply: A Modeling Study. The Lancet. 2016. Publisher's VersionAbstract

Background The ongoing yellow fever (YF) epidemic in Angola strains the global vaccine supply, prompting WHO to adopt dose sparing for its vaccination campaign in Kinshasa in July-August 2016. Although a 5-fold fractional-dose vaccine is similar to standard-dose vaccine in safety and immunogenicity, efficacy is untested. There is an urgent need to ensure the robustness of fractional-dose vaccination by elucidating the conditions under which dose fractionation would reduce transmission.

Methods We estimate the effective reproductive number for YF in Angola using disease natural history and case report data. With simple mathematical models of YF transmission, we calculate the infection attack rate (IAR, the proportion of population infected over the course of an epidemic) under varying levels of transmissibility and five-fold fractional-dose vaccine efficacy for two vaccination scenarios: (i) random vaccination in a hypothetical population that is completely susceptible; (ii) the Kinshasa vaccination campaign in July-August 2016 with different age cutoff for fractional-dose vaccines.

Findings We estimate the effective reproductive number early in the Angola outbreak was between 5.2 and 7.1. If vaccine action is all-or-nothing (i.e. a proportion VE of vaccinees receives complete and the remainder receive no protection), n-fold fractionation can dramatically reduce IAR as long as efficacy VE exceeds 1/n. This benefit threshold becomes more stringent if vaccine action is leaky (i.e. the susceptibility of each vaccinee is reduced by a factor that is equal to the vaccine efficacy VE). The age cutoff for fractional-dose vaccines chosen by the WHO for the Kinshasa vaccination campaign (namely, 2 years) provides the largest reduction in IAR if the efficacy of five-fold fractional-dose vaccines exceeds 20%.

Interpretation Dose fractionation is a very effective strategy for reducing infection attack rate that would be robust with a large margin for error in case fractional-dose VE is lower than expected.

2015
Measuring the Association between Artemisinin-Based Case Management and Malaria Incidence in Southern Vietnam, 1991–2010
Peak CM, Thuan PD, Britton A, et al. Measuring the Association between Artemisinin-Based Case Management and Malaria Incidence in Southern Vietnam, 1991–2010. American Journal of Tropical Medicine and Hygiene. 2015;92 (4) :811-817. Publisher's VersionAbstract

In addition to being effective, fast-acting, and well tolerated, artemisinin-based combination therapies (ACTs) are able to kill certain transmission stages of the malaria parasite. However, the population-level impacts of ACTs on reducing malaria transmission have been difficult to assess. In this study on the history of malaria control in Vietnam, we assemble annual reporting on malaria case counts, coverage with insecticide-treated nets (ITN) and indoor residual spraying (IRS), and drug purchases by provincial malaria control programs from 1991 to 2010 in Vietnam’s 20 southern provinces. We observe a significant negative association between artemisinin use and malaria incidence, with a 10%absolute increase in the purchase proportion of artemisinin-containing regimens being associated with a 29.1% (95% confidence interval: 14.8–41.0%) reduction in slide-confirmed malaria incidence, after accounting for changes in urbanization, ITN/IRS coverage, and two indicators of health system capacity. One budget-related indicator of health system capacity was found to have a smaller association with malaria incidence, and no other significant factors were found. Our findings suggest that including an artemisinin component in malaria drug regimens was strongly associated with reduced malaria incidence in southern Vietnam, whereas changes in urbanization and coverage with ITN or IRS were not.