Disease outbreak news: Yellow fever – Nigeria (24 November 2020)

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Reports of a cluster of deaths from an undiagnosed disease were notified on 1 November 2020 through Event Based Surveillance in two states, Delta and Enugu, located in southern Nigeria. The Delta State health surveillance system had been informed of the outbreak on 30 October 2020, following a cluster of deaths presenting with similar symptoms.

On 2 November 2020, the Nigeria Centre for Disease Control (NCDC) reported to WHO a cluster of deaths in Ute Okpu community in Ika North-East local government area (LGA) of Delta State. Additional cases were reported from 4 other wards of Ika North-East (Idumessah, Owa Alero, Owanta, and Umunede). A preliminary report for Delta State on 5 November 2020, notified of 48 suspected cases of yellow fever (YF) with 30 deaths (CFR 62.5%). The most frequent symptoms included 1-week history of fever, vomiting (with or without blood), bleeding, seizures, and unconsciousness. One patient was reported to have cough, sore throat, and hiccups. Of those 48 reported cases, the main occupation was farmers, and males were predominantly affected (75%). The YF vaccination status of most of the suspected cases is unknown. The index case developed symptoms on 24 July 2020 and died on 28 July 2020. Preliminary investigation did not reveal any significant travel history. Two blood samples were collected, along with nasal and throat swabs on 31 October 2020. Laboratory investigations were carried out at the mobile laboratory of Irrua Specialist Teaching Hospital (ISTH) in Delta State. All blood samples tested by polymerase chain reaction (PCR) were negative for Lassa fever and the throat swab was negative for severe acute respiratory syndrome coronavirus 2 . Six more blood samples were collected and sent to ISTH, Edo State and all were negative for Lassa fever, while three were positive for YF by PCR. As of 10 November 2020, 65 suspected cases, including 33 deaths, have been reported. Samples were collected from 27 cases and seven have tested positive for yellow fever by PCR.

On 4 November 2020, the Enugu State epidemiologist reported a cluster of deaths of unknown cause to NCDC. Investigations by the Rapid Response team for Enugu State on 4 November 2020 reported 10 deaths, with the majority being males aged 4 to 65 years old and with occupations as farmers. The most frequent symptoms included high grade fever, convulsion, and eventually coma, in addition to blood in the urine, mouth bleeding, bleeding in the respiratory tract, blood shot eyes and pain in the flank. The suggestive differential diagnosis was Lassa fever, YF, cerebrospinal meningitis and COVID-19. A total of 13 blood samples were collected and sent to the National Reference Laboratory in Abuja to be tested for viral haemorrhagic fevers. Results received on 10 November 2020 showed 6 PCR positive YF cases in Enugu State.

On 8 November 2020, Bauchi State reported 8 samples tested by PCR at the NCDC National Reference Laboratory positive for YF (7/8 from Ganjuwa LGA, 1/8 unknown LGA). Four of these samples were also IgM positive for YF. Detailed case investigations are ongoing, and the line list is currently being updated.

On 15 November 2020, 3 PCR positive samples for yellow fever were reported from Ogbadibo LGA in Benue State. These samples were also tested at the NCDC, National Reference Laboratory. Additionally, there has been a PCR positive sample for YF reported from Ohaukwu LGA in Ebonyi State. This LGA has also been the location of a cluster of probable YF cases that were IgM positive at national reference laboratory and had dates of onset July-August 2020. Security challenges in the LGA had hindered full investigation and work-up at the time of initial notification.

Nigeria is facing concurrent outbreaks of multiple pathogens. Delta State, located in the South-South geo-political zone of the country, is one of the Lassa fever affected states, though not considered one of the YF hot spot states. In 2020, 18 Lassa fever cases have been laboratory confirmed from 140 suspected cases, including 3 fatalities. Enugu state, in the South-East geopolitical zone of the country, shares boundaries with Benue (Ogbadibo LGA) where there are 3 confirmed cases of Lassa fever, and Ebonyi state which is one of the hotspot states for the Lassa fever outbreak. To date, 10 Lassa fever cases have been reported from Enugu state since the start of the year, including 2 fatalities (20% CFR). While Lassa fever cases are reported year-round, the peak period is December to April.

The relative proximity of Delta, Enugu, Benue and Ebonyi states with Lagos is an added concern, though population movements (and hence risk of spread) may have been reduced in the COVID-19 context. However, there is a lack of data on this, and the risk of spread should be monitored.

COVID-19 response efforts demand an extraordinary amount of time and resources from the country’s health system while lockdowns, travel restrictions and other mitigations to slow the spread have severely disrupted access to core essential health services. National and state authorities are currently focused on the COVID-19 pandemic, limiting the human resources required to conduct investigations and response activities for the YF outbreaks. Recent relaxation of COVID-19 measures will increase population mobility thereby increasing the risk for amplification of yellow fever, especially if introduced into urban centres. Population mobility in urban settings can be particularly challenging in conducting mass vaccination campaigns due to the size and diagnostic challenges of the operation (SAGE 2016). As of 23 November 2020, 66 383 COVID cases, including 1 167 deaths, have been reported in Nigeria.