Characterisation of Vibrio cholerae isolates from the 2009, 2010 and 2016 cholera outbreaks in Lusaka province, Zambia

Abstract

In the last three decades, Zambia has experienced frequent cholera outbreaks which mainly affect fishing camps around the country and peri urban areas in Copperbelt and Lusaka Provinces where there is unsafe water supply and poor sanitation. In 2009, 2010 and 2016 more than 12000 cases, with about 300 deaths, were reported from Zambia with Lusaka reporting more cases than the rest of the country. However, the antibiogram and genetic diversity of the Vibrio cholerae isolates causing these outbreaks in Lusaka Province were unknown. This knowledge is essential to inform cholera prevention and control programmes. This was a laboratory based cross-sectional study that sought to determine the antibiogram and genetic diversity of Vibrio cholerae isolates from the 2009, 2010 and 2016 cholera outbreaks in Lusaka Province. All available isolates from the respective outbreaks were included in this study and they were characterised by serotyping, antimicrobial susceptibility testing and macro-restriction analysis using Pulsed-Field Gel Electrophoresis. The 2009 and 2016 outbreaks yielded only the Ogawa serotype, while the 2010 outbreak only yielded the Inaba serotype. All the isolates were 100% resistant to nalidixic acid and nitrofurantoin. The 2009 and 2010 cholera outbreak isolates showed 100% multidrug resistance while 67 % of 2016 were multidrug resistant. Macrorestriction analysis demonstrated high diversity among the isolates with six clusters of at least 92% similarity. The largest cluster comprised 12 isolates with 97.8-100% similarity, while the smallest cluster comprised 3 isolates with 95.3-98% similarity. This study demonstrated that both the Inaba and Ogawa serotypes were responsible for the cholera outbreaks with only one of the serotypes responsible for each particular v outbreak; 2009(Ogawa), 2010(Inaba) and 2016(Ogawa). The study also revealed multidrug resistant Vibrio cholerae strains circulating in all the three outbreaks. Macrorestriction analysis demonstrated high genetic diversity among the Vibrio cholerae isolates, suggesting that the isolates were not from the same source of infection. The findings in this study will be used to guide therapy and track the sources and spread of infection for effective cholera management. There is need to establish a national surveillance system for cholera to monitor antibiotic resistance and to track the virulence and antibiotic resistance genes of Vibrio cholerae strains circulating in Zambia to gain insight into their clinical implications.