Cholera remains a global threat to public health and a key indicator of lack of social infrastructural development. The re-emergence of cholera has been associated with the ever-increasing size of vulnerable populations living in unsanitary conditions (WHO, 2017). In an epidemic, the great majority of cases can be easily recognized by clinical diagnosis and a bacteriological diagnosis is often not required (Azman et al., 2013).
Cholera has a significantly destructive impact on populations (WHO, 2005). Cholera is found in many tropical countries around the world including most of Africa (Gidado et al., 2018). Between 1970 and 1974, Sub-Saharan African countries reported a total of 103,000 Cholera cases (WHO, 2005). In 2005, approximately 1,000,000 people developed cholera of which about 100,000 died (WHO, 2005). A total of 131,943 cases including 2,272 deaths were notified from 52 countries in 2005. The year 2005 was marked by a particular series of outbreaks in West Africa, involving 14 countries which accounted for 58% of all cholera cases worldwide (WHO, 2005).
Although reports of a cholera epidemic in Nigeria have not been consistent, the disease is very dynamic. The emergence of cholera was first evident in 1970 and later reemerged in 1991. During the last two decades, three major epidemics have occurred; in 1992 (Umoh et al., 1983), 1995/1996 (Hutin et al., 2003), and 1997 (Usman et al., 2005).
In 2017, 1,200,000 cases were reported in Asia and it was the highest value recorded in 29 years (Figure 1)
Figure 1: A chart showing the Cholera cases reported to WHO by year and by continent from 1989 to 2017
The Situation of Cholera in Nigeria
Cholera is endemic in Nigeria, and there was an increase in reported cases in June 2021. Following this rise in infections across the country, the Nigeria Centre for Disease Control (NCDC) activated a comprehensive cholera Emergency Operations Centre (EOC) on the 21st of June, 2021. As of the 24th of October 2021, there were 93,932 suspected cases and 3,293 associated deaths in Nigeria (ACAPS, 2021). These numbers put the case-fatality rate at 3.5%, which was higher than the previous annual outbreaks in the past four years. The outbreak affected 32 of the 36 states of the country, including the Federal Capital Territory (FCT) Abuja. Children aged 5–14 were the most affected age group. Northern Nigeria was the most affected region, with 89% of all suspected cholera cases. 57% of the cumulative suspected cases were reported in four states in northern Nigeria: Bauchi (19,452), Kano (12,116), Zamfara (11,100), and Jigawa (10,763), as seen in figure 1 (NCDC, 2021).
Historically, Northern Nigeria has been known to be a cholera-endemic region. Epidemiological data from the Public health department of the Kano State Ministry of Health, Nigeria, revealed that the frequency and distribution of recurrent cholera epidemics in the state from 1995 to 2001, were 2,630 in 1995/1996, 847 in 1997 and 2,347 in 1999 (Usman et al., 2005). In Jos, North Central Nigeria, Opajobi et al., (2004) observed that all isolated strains were Vibrio cholerae O1 Eltor of Inaba serotype. The authors concluded that Vibrio cholerae O1 is endemic in Jos, Nigeria (Opajobi et al., 2004).
Figure 2: A map showing the states in Nigeria affected by the cholera outbreak as of October 2021 (ACAPS, 2021)
As of the 2nd of January 2022, a total of 111,062 suspected cases including 3,604 deaths (CFR 3.2%) were reported from 33 states and the FCT in 2021. Among the suspected cases since the beginning of the year 2021, the age group 5 – 14 years was the most affected age group for males and females with an equal distribution of 50% males and 50% females. Four states – Bauchi (19,558 cases), Jigawa (15,141 cases) Kano (12,116 cases), and Zamfara (11,931 cases) accounted for 53% of all cumulative cases and eleven local government areas (LGAs) across five states Bauchi (4), Zamfara (4), Kano (1), Katsina (1) and Borno (1) reported more than 1,000 cases each in the year 2021.
As seen in figure 3 below, The highest number of cholera cases in the year 2021 was reported in week 33 with over 9,000 cases reported; while week 52 had the lowest reported number of 46 cases.
Figure 3: A chart showing the National Epidemic curve of weekly reported Cholera cases, week 1 to week 52, 2021 (NCDC, 2021)
Figure 4: A chart showing the number of cumulative Cholera cases with case fatality ratio (CFR) by state, week 1 – 52, 2021 (NCDC, 2021)
As shown in figure 4 above, Bauchi state had the highest number of cases in the year 2021 with a case fatality ratio of 24.0%. Akwa Ibom state was the least affected with a case fatality ratio of 0.0%.
|S/N||State||Cases||% of Cumulative cases||Cumulative % of total cases|
In January 2022, a total of 470 suspected cases including 9 deaths (CFR1.9%) were reported from 10 states. Among the suspected cases since the beginning of the year, the age group < 5 years was the most affected age group for males and females, with 45% being males and 55% females. Three states -Taraba (201 cases), Borno (88 cases) and Adamawa (56 cases) accounted for 73% of all cumulative cases. Ten LGAs across five states Borno (3), Adamawa (2), Taraba (1), Bayelsa (1) and Kwara (1) reported more than 10 cases each this year.
|S/N||State||Cases||% of Cumulative cases||Cumulative % of total cases|
The highest number of deaths from cholera was reported in week 2 (5 deaths) and no death was reported in week 3 as shown in figure 5 below.
Figure 5: A chart showing trends in deaths of weekly reported Cholera cases, week 1-week 4, 2022 (NCDC, 2022)
Figure 6: Map of Nigeria showing suspected cases across states with RDT + Culture, week 1-4, 2022 (NCDC, 2022)
Figure 7 shows that in the first 4 weeks of the year 2022, Taraba state reported the highest number of Cholera cases with a case fatality ratio of 14%.
Figure 7: A chart showing the number of cumulative cholera cases with case fatality ratio (CFR) by state, week 1-4, 2022 (NCDC, 2022)
Mode of Diagnosis of Cholera and risk factors for transmission in Nigeria
Cholera is transmitted by the faecal-oral route, usually after ingestion of food or water that has been contaminated with infected faeces. Other common vehicles of infection include contaminated fish and shellfish, and left-over cooked grains that have not been reheated properly (Ryan et al., 2018). Direct person-to-person transmission of cholera is rare, as a high infectious dose of 108 bacteria is necessary to cause the disease in healthy individuals, but a much lower dose (105) is sufficient in individuals with low levels of gastric acid (Zhang et al., 2003).
Cholera can be confirmed by culture of stool or rectal swab specimens, followed by serological testing with O1 or O139 antisera. Further characterization of serotypes can be performed using antisera on serotypes Inaba and Ogawa (Feglo and Sewurah, 2018). Commercially available rapid diagnostic test kits are convenient for use in epidemic settings. However, they do not yield an isolate for antimicrobial susceptibility testing and sub-typing and should not be used for routine diagnosis (WHO, 2018).
For a cholera outbreak to occur, two conditions have to be met: (1) there must be significant breaches in the water, sanitation, and hygiene infrastructure used by groups of people, permitting large-scale exposure to food or water contaminated with Vibrio cholera organisms; and (2) Cholera must be present in the population (WHO, 2019).
In Nigeria, the 1996 cholera outbreak in Ibadan (Southwest) was attributed to contaminated potable water sources (Lawoyin et al., 1999). Street-vended water and not washing hands with soap before eating food were possible reasons for the 1995-1996 cholera outbreaks in Kano state (Lipp et al., 2002). Drinking water sold by water vendors in Ibadan was also connected with an increased risk of contracting the disease (Lawoyin et al., 1999). In Katsina, the outbreak of the disease was linked to faecal contamination of well water from sellers (Umoh et al., 1983). The 2010 outbreak of cholera was speculated to be directly related to sanitation and water supply. The hand-dug wells and contaminated ponds being relied on by most of the Northern states as a source of drinking water were major transmission routes during the outbreak. Perhaps, these wells were shallow; uncovered and diarrhoea discharge from cholera patients could easily contaminate water supplies (Igomu, 2011).
Adeneye et al., (2016) conducted a study to investigate the risk factors associated with the cholera epidemic during the 2010 outbreak in some states in Nigeria. Semi-structured questionnaires were administered to consenting parents and/or their parents/guardians in Bauchi and Gombe States in North-East Nigeria. Few (33.7%) respondents had access to safe and clean drinking water through the pipe-borne system as compared to wells (47.8%) and rivers (19.6%). Respondents’ means of sewage disposal were: pit/latrine (77.2%); bush (15.2%); and water closet (4.3%). Results from observations showed poor sanitation and food hygiene practices in the communities visited. The results provided insights for planning educational programmes through information, education and communication/behavioural change communication efforts to boost knowledge on cholera in the communities.
Management and Prevention/Control of Cholera
The mainstay of the case management of cholera is the treatment of dehydration using Oral Rehydration Therapy (ORS) or IV fluids (Ringer lactate) and electrolytes (Mafi et al., 2016 and NCDC, 2021).
In cholera management, antibiotic prophylaxis is usually not part of the intervention but is essential for disease treatment in severe cases. However, Vibrio cholera strains from endemic and outbreak situations within the last decade revealed interesting patterns of antibiotic resistance to commonly used antimicrobial agents (Kotsiou et al., 2017). Mobile genetic elements able to transfer multiple drug resistance among Vibrio cholera strains have been described in numerous studies and are considered a major public health problem (Coppo et al., 1995; Kotsiou et al., 2017).
The obvious emergence of resistant strains could be correlated with widespread therapeutic and prophylactic administration of antibiotics, especially tetracycline and their availability over the counter. While continued misuse of antibiotics has indubitably contributed to the endemic nature of most infections, the recent cholera outbreak experience proposes that other factors also play a role in determining whether a particular strain (or resistance plasmid) remains in a given geographic area. Studies are however needed in this area to elucidate this concept (Jeandron et al., 2018).
In Nigeria, existing prevention and control strategies are multi-sectorial. Epidemic Preparedness and Response (EPR) approaches including registration of cases, case management and public health measures targeting personal hygiene and water treatment, as well as emergency responses from both governmental and non-governmental agencies, have contributed to the reduction in case-fatality rates over the years and should be sustained (Gidado et al., 2018). Nevertheless, the need to explore more viable approaches cannot be overplayed if the infection has to be wholly curtailed (Gidado et al., 2018).
Various studies elsewhere have utilized geographic and mathematical information systems to assess the spatial distribution of cholera at local levels, demonstrating case clustering and disease risk areas (Tuite et al., 2011). Modelling techniques using climate data, remote monitoring, and geographic information systems also provide new techniques that may contribute to the prediction of cholera epidemics (Colwell, 1996, Feglo and Sewurah, 2018). According to Feglo et al., (2018) such models can aid understanding of epidemic processes and help design effective control strategies. Due to its endemic nature in Nigeria, surveillance systems can provide early alerts to outbreaks, therefore leading to a coordinated response.
Understanding the seasonality and location of outbreaks may also provide guidance for improving cholera control activities in vulnerable areas. Vigorous health promotion activities in terms of continuous public enlightenment on cholera are evidently essential to controlling the infection. There should also be an improvement in surveillance systems, communication and transport (NCDC, 2018). In addition, mechanisms for quick intervention should be put in place, also other health system components need to be strengthened with the provision of adequate manpower, equipment, drugs and consumables (Ogbeyi et al., 2017). Defining strain diversity using molecular biology techniques may also assist with describing the intrinsic characteristics of diseases, such as the persistence of infection. The knowledge of the interaction of strain variants may also be a critical option for controlling the infection since molecular biology techniques are accessible. This can improve prevention plans, as well as risk assessment for potential cholera outbreaks (NCDC, 2018).
The NCDC response to the 2022 outbreak of cholera is being coordinated by the National Multi-sectoral technical working group (TWG) hosted by the NCDC in collaboration with the Federal Ministry of Health (FMoH), Federal Ministry of Water Resources (FMWR), Federal Ministry of Environment (FMEnvrt) and partners to continue training on cholera surveillance, hotspot mapping, and develop state-level preparedness and response plans; also to maintain communication with support states for data reporting and response and continue advocacy to State Governments to increase funding for water, sanitation and hygiene (WASH) infrastructure (NCDC, 2022).
The NCDC has stated that response commodities will be pre-positioned across states, capacity building will be carried out for sample collection, transportation and laboratory diagnosis, Planned After Action Review (AAR) and risk communications will be scaled up (NCDC, 2022).
Above all, the World Health Organization (WHO) recommends that immunization with currently available cholera vaccines be used in conjunction with the usually recommended control measures in areas where cholera is endemic as well as in areas at risk of outbreaks (WHO, 2021).
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