Background

Avian influenza (AI) is a viral disease that infects bird species, with varying levels of severity, depending on the virus strain involved. The viruses with H5 or H7 surface proteins cause the most severe form of AI, and are described as the highly pathogenic avian influenza (HPAI) [1]. Wild birds are the common vectors of the AI viruses. The virus is however highly contagious among domesticated birds, including chickens, ducks, and turkeys. The infection occurs when a bird directly comes in contact with other infected birds, or indirectly through contact with contaminated water, feed, and surfaces. The HPAI may cause disease affecting multiple internal organs, with a 48-hour mortality rate ranging between 90-100% [2].
According to the World Health Organization (WHO) and International Organization for Animal Health (OIE), human infections with AI viruses have been sporadic globally, a majority of which originated from Asia [3,4]. However, person-to-person transmission of AI viruses is rarely reported. The risk of AI infection of humans remains high if biosafety measures are neglected, and is mainly related to outbreaks among poultry [5]. Most of the AI outbreaks in humans result from close contact with sick domesticated birds [6]. The ability of AI viruses to cross the species barrier is high because they are constantly evolving through mutation and genetic re-assortment leading to the emergence of new subtypes, thereby posing significant threat to both animal and human health [7].
The AI viruses that have crossed the species barrier to infect humans include A(H5N1), A(H5N6), A(H7N4), A(H7N9), and A(H9N2). Since its emergence in China in 2013, the outbreaks of A(H7N9) has infected more humans (excess of 1500 human cases) than any of the other types. However, A(H5N1) has caused the largest number of cases of severe disease and death in humans [2,4]. According to the WHO, more than 860 human cases of A(H5N1) virus were reported from 17 countries globally, with more than 50% case fatality rate between January 2003 and December 2019 [4]. 
In many African countries, outbreaks of HPAI A(H5N1), A(H5N2) and A(H5N8) in poultry have been confirmed [3]. The first of the infection in Africa occurred in Nigeria in 2006, which subsequently spread quickly to at least 17 other countries on the continent by 2017 [7,8]. Only three African countries including Djibouti, Nigeria, and Egypt reported confirmed human cases of HPAI A(H5N1) on the continent since its first confirmation in 2006 [7]. The first human case of HPAI A(H5N1) was confirmed on March 20, 2006 in Egypt. By November 2010, more than 100 human cases were confirmed in Egypt with majority of the confirmed cases linked to contact with poultry kept in backyard farms [9]. Globally, Egypt recorded the highest number of 346 confirmed human cases by the end of 2015 [7].
Ghana reported its first confirmed HPAI A(H5N1) outbreak in poultry in 2007 in three regions including Greater Accra, Volta, and Brong Ahafo Regions. Until 2015, no outbreaks of HPAI were reported, with the Greater Accra Region first confirming cases of H5N1 in April 2015. Subsequently, five of the sixteen regions in Ghana, also recorded confirmed cases by June the same year, affecting both commercial and free-range poultry farms and leading to losses of approximately 100,000 birds [10]. Between 2017 and 2018, the A(H9N2) strain was identified in outbreaks in poultry in the Ashanti and Brong-Ahafo Regions of Ghana [11]. The spread of AI in Ghana has mainly been attributed to poor biosafety practices on farms and poor regulation of movement of live poultry [10]. No human cases of HPAI have been confirmed in Ghana since its introduction in 2007 [7]. 
On June 21, 2018, a farm owner notified the Veterinary Office in the Kwahu West Municipality of the death of birds on his small-scale commercial poultry farm at Nkawkaw. A different small-scale commercial farm located about 100 meters from the index-case farm also started recording deaths of birds 7 days later. Upon visiting the farms, the Municipal Veterinary Officers suspected a HPAI outbreak. Based on their notification, the Eastern Regional Health Directorate through the Municipal Health Management Team (MHMT), constituted a team to respond to the outbreak. We investigated the outbreak to confirm the causative agent, identify its source, assess risk factors for spread, and implement control measures.