Early Release – Chikungunya Outbreak in Country with Multiple Vectorborne Diseases, Djibouti, 2019-2020 – Volume 29, Number 4 – April 2023 – Emerging Infectious Diseases journal

Disclaimer: Articles in pre-release versions are not considered final versions. Any changes will be reflected in the online version in the month the article is officially published.

Emilie Javelle, Franck de Laval, Guillaume André Durand, Aissata Dia, Cécile Ficko, Aurore Bousquet, Deborah Delaune, Sébastien Briolant, Audrey Mérens, Constance Brossier, Hervé Pommier, Florian Gala, Alain Courtiol, Quentin Savreux, Sébastien Sicard, Jean-Philippe Sanchez, Francis Robin, Fabrice Simon, Xavier de Lamballerie, Gilda Grard, Isabelle Leparc-Goffart, and Vincent Pommier de Santi

Author Affiliations: French University of Aix Marseille, Marseille, France (E. Javelle, GA Durand, S. Briolant, F. Simon, X. de Lamballerie, G. Grard, I. Leparc-Goffart, V. Pommier de Santi); French Armed Forces Biomedical Research Institute, Marseille (E. Javelle, GA Durand, S. Briolant, G. Grard, I. Leparc-Goffart); University Hospital Institute-Méditerranée Infection, Marseille (E Javelle, S Briolant); French Military Center for Epidemiology and Public Health, Marseille (F. de Laval, A. Dia, C. Brossier, S. Sicard, V. Pommier de Santi); Bégin Military Teaching Hospital, Saint Mandé, France (C Ficko, A Bousquet, A Mérens, A Courtiol); Armed Forces Biomedical Research Institute, Brétigny-sur-Orge, France (D. Delaune); French Military Health Service, Djibouti City, Djibouti (H. Pommier, F. Gala, Q. Savreux, J.-P. Sanchez, F. Robin)

Djibouti is a semi-arid country bordering Eritrea, Somalia and Ethiopia. In the region, the main vector of chikungunya virus (CHIKV) and dengue virus (DENV) is the Aedes aegypti mosquito. French forces are stationed in Djibouti City, where 70% of the country’s population lives (total population ≈ 900,000). Military bases and accommodation are located in the urban area and the entire French Defense Community (FDC), including military personnel, families and civilian employees, comprises a population of 2,700.

From July to October 2019, a large-scale Chikungunya outbreak (41,162 suspected cases, 16 laboratory-confirmed cases, attack rate 12.3%) occurred in Dire Dawa, Ethiopia, 260 km from Djibouti city (Figure 1 attached) (1st ). In a 2010–2011 survey in Djibouti City, 2.6% of the population had serological evidence of CHIKV infection (2), although no epidemic has been reported since then (2). Given the road, rail and air links between the two cities and the CHIKV-naïve local population, we assessed the probability of a CHIKV outbreak in Djibouti City as very likely. Patient management was a challenge as dengue fever and malaria are endemic in Djibouti (3).

We describe the FDC’s comprehensive response to these multiple vector-borne diseases and evaluate the use of blood on blotter paper for arboviral diagnosis. With patient consent, we collected and anonymized epidemiological and clinical data for diagnostic purposes. Because this outbreak was considered an imminent threat to public health under French regulations, no ethical approval was required for this investigation.

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illustration 1

Figure 1. Flowchart for Arboviral Disease Diagnosis in French Defense Community in Djibouti, 2019-2020. *The number of samples tested was limited due to the introduction of whole blood RT-PCR in Djibouti city 1 month…

In October 2019, we increased epidemiological surveillance at the FDC to detect the emergence of CHIKV. We defined a suspected case of arbovirus-like disease (ALD) as fever or chills and/or acute arthralgia and/or rash and/or vomiting and diarrhea. Symptomatic patients were encouraged to see a doctor to be systematically tested for dengue, chikungunya and malaria. We collected venous blood from each person with ALD signs/symptoms, blotted it onto Whatman 3MM blotting paper (Sigma-Aldrich, https://www.sigmaaldrich.com), dried the samples at room temperature, and stored them in a sealed plastic bag for storage and transportation (4). The National Arbovirus Reference Center in France performed reverse transcription-PCR (RT-PCR) and serological testing for CHIKV and DENV on blotting paper, as described elsewhere (5). In January, on-site equipment was set up to perform in-house RT-PCR for DENV and CHIKV on whole blood samples (Figure 1) (6,7). Chikungunya cases were confirmed by positive RT-PCR on whole blood or blotting paper, or by detection of CHIKV-IgM on blotting paper. Dengue cases were confirmed by a positive DENV RT-PCR on whole blood or blotting paper or a positive nonstructural protein 1 (NS1) antigen rapid diagnostic test (RDT) (Bioline Dengue Duo; Abbott, https://www.abbott.com) . We provided care according to French national recommendations (8) and World Health Organization guidelines (9). At the same time, we have strengthened the following measures in the FDC vector control measures and personal protection: larvae source management, long clothing, insect repellent and long-lasting insecticide nets.

figure 2

Figure 2. Vector-borne diseases in the French defense community in Djibouti: epidemic trajectory and availability of diagnostic tools, 2020 (Chikungunya = 58, Dengue = 56 and Malaria = 6 cases). NS1, not structural…

We compared clinical presentations of dengue and chikungunya using software R version 3.5.1 (The R Project for Statistical Computing, https://www.r-project.org) for statistical analysis. Overall, among the 2,700 people in the FDC, we included 282 with ALD. As of March 2020, we confirmed 120 cases of vector-borne diseases (attack rate 42.6%, 120/282): 58 Chikungunya (2.1%, 58/2,700), 56 Dengue (2.1%), 6 Malaria (5 Plasmodium falciparum and 1 P. vivax) and no coinfections (Figure 2). We also documented 2 concurrent influenza A virus and arbovirus infections. Among patients with vector-borne diseases, 67.5% (81/120) were male and 73.3% (88/120) were military personnel. The median age was 34.5 (range 8.3-79.6, interquartile range 27.1-40.0) years, and 92.5% (111/120) of subjects sought medical help within 48 hours of symptom onset Help on (median 1, range 0-7, interquartile range 0-1 day).

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We confirmed the first case of chikungunya in individuals in the FDC in November 2019. The outbreak began in December and lasted 13 weeks. The CHIKV strain belonged to the Indian lineage of the East/Central/South African genotype (10). The dengue outbreak peaked in late January and was associated with DENV-1 with a unique serotype that was confirmed for 36/56 dengue cases (Figure 2). CHIKV and DENV circulated together for 16 weeks. One Chikungunya case was diagnosed only by CHIKV-IgM on blotting paper; all others (57/58, 98%) were confirmed by RT-PCR. One case of dengue was diagnosed by positive NS1 antigen RDT with positive DENV IgM on blotting paper; all others (55/56, 98%) were confirmed by RT-PCR (Figure 1). The National Reference Center obtained blotter samples for 93.0% (106/114) of DENV and CHIKV infections and confirmed 97.2% (103/106) of diagnoses, 93.4% (99/106) by RT-PCR and 3.8% (4/106) by serology (1 DENV and 3 CHIKV). DENV and CHIKV RT-PCR testing was performed on both whole blood and blotting paper at 44.7% (51/114) (Tables 1, 2). Compared to RT-PCR of whole blood, no RT-PCR of blotting paper gave false positive results.

Samples from ALD patients were tested locally with NS1 antigen RDT and 43 (43/120, 36%) results were positive. Results were negative in 13/56 (23%) individuals with dengue, all of whom were tested within a median delay of 1.5 (range 0-3) days after symptom onset. Among the 46 with DENV infection confirmed by whole blood RT-PCR, 36 (78%) had co-positive RDT results.

The main ALD sign was fever (90.8%, 109/120). Headaches and digestive disorders were more frequently associated with dengue fever (odds ratio [OR] 7.2, 95% CI 2.3-22.8) than Chikungunya (OR 5.9, 95% CI 1.8-19.6) (table attached). Arthralgia of the toe (OR 29.97, 95% CI 3.19-195.61), ankle (OR 18.28, 95% CI 6.14-54.71), finger (OR 12, 47, 95% CI 3.93-39.61) and wrist (OR 12.47, 95% CI 3.93-39.61). OR 18.27, 95% CI 5.71-58.52). Secondary infection developed in 4 patients with Chikungunya (1 each of pneumonia, dysentery, recurrent herpes, and gingivitis with oral candidiasis). Among the dengue patients, 4 had hepatic cytolysis (maximum elevation of transaminases 12-fold upper limit) and 3 had secondary infections including acute pneumonia, Escherichia coli pyelonephritis, and intestinal amebiasis. No patient met criteria for severe dengue fever. No ALD patient required critical care. All malaria patients recovered after 3 days of treatment with artenimol/piperaquine and secondary treatment with primaquine for the patient with P. vivax infection. Treatment of arboviral diseases has relied primarily on analgesics, antihistamines, and hydration. Prescribing nonsteroidal anti-inflammatory drugs, aspirin, or corticosteroids was formally contraindicated during the first few days of infection. In patients with confirmed chikungunya, we carefully assessed the benefit-risk balance of introducing nonsteroidal anti-inflammatory drugs.

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Despite recent improvements in diagnostic tools, Chikungunya outbreaks in Africa are likely to be underreported (11). A large-scale chikungunya outbreak occurred in Djibouti City in 2019–2020 (12). However, due to a lack of diagnostic tests and dedicated reporting, no data are available to estimate the extent. The chikungunya outbreak remained limited in the FDC (attack rate 2.1%), but was followed by a dengue outbreak. We found that clinical features are helpful but not sufficient to differentiate between chikungunya and dengue (13,14). Biological confirmation remains necessary to determine appropriate care. The use of blood samples on blotting paper has been described as a field method for arbovirus detection (4,5), routinely used by the French armed forces during operations in Africa (15). In this study, we used blood samples on blotting paper to detect the occurrence of CHIKV and to monitor the course of outbreaks. Blotting paper provided a robust method for blood collection and transport to a reference laboratory, confirming 90% of arboviral diagnoses. We recommend blotting paper as an on-site tool to remotely detect and monitor arboviral epidemics.

dr Javelle is a military doctor and specialist in infectious diseases at the Laveran Military Teaching Hospital and researcher at the Biomedical Research Institute of the French Armed Forces and at the Institut Méditerranée-Infection of the University Hospital in Marseille, France. She has clinical and scientific experience in the fields of vector-borne diseases and travel medicine.