Cholera in Lusaka, Zambia, 2017–2018: Chlorine, Vaccine and a Flood-Driven Return

Cholera strikes an estimated 2.9 million people a year in countries where it is endemic, and 1.3 billion are at risk, usually through contaminated drinking water. On October 6, 2017, Zambia declared an outbreak after two patients who visited a clinic in the capital, Lusaka, tested positive for Vibrio cholerae O1 (El Tor, serotype Ogawa).

The outbreak

Cases climbed from several hundred in early December 2017 to about 2,000 by early January 2018. By May 12, 2018, the outbreak had reached 7 of Zambia's 10 provinces, with 5,905 suspected cases and a case fatality rate of 1.9%. 5,414 (91.7%) of the cases, and 98 deaths, were among Lusaka residents.

Reported cholera cases and related events, by week, Lusaka, Zambia, October 2017–May 2018. CDC / MMWR

The outbreak centered on Lusaka's peri-urban areas, home to about 60% of the city, with little access to municipal water or sewers. Zambia's first cholera outbreak came in 1977–1978, and outbreaks of about 11,000 cases struck in 1991, 1992 and 1999.

What investigators found

The Ministry of Health worked with the Zambia National Public Health Institute, the Zambia Field Epidemiology Training Program, CDC, the World Health Organization and Africa CDC.

• Beliefs: in a December 2017 survey of 267 households in the worst-hit areas, 58% thought poor hygiene caused cholera, and 63% named contaminated water as a risk.
• Risk factors: a study of 81 patients and 130 controls found higher odds of cholera after contact with a sick person (odds ratio 6.6) or drinking untreated water (3.6), and lower odds for women (0.3).
• Deaths: of Lusaka's 98 deaths, 58 (59%) happened at home in the community and 40 (41%) at cholera treatment centers. Staying one more night at a treatment center cut the odds of dying (odds ratio 0.30) — access to care, including rehydration, saves lives. Community reports suggest stigma about being linked with poor hygiene may have delayed people seeking care.
• Water: of 220 randomly chosen drinking water sources tested in January 2018, 160 (73%) had too little chlorine (under 0.2 mg/L), and many of those carried E. coli, a sign of fecal contamination — most often shallow wells (91%) and boreholes (34%).
• Laboratory: of 2,054 stool samples, 925 (45%) grew V. cholerae O1, nearly all Ogawa (five Inaba). All 50 isolates tested were sensitive to cotrimoxazole, tetracycline, chloramphenicol and azithromycin; for ampicillin, 72% were sensitive. First-line treatment was doxycycline for adults and cotrimoxazole for children.

The response

A national emergency operations center coordinated the government and partners including UNICEF, WHO, the Zambia Red Cross and Médecins Sans Frontières.

• Safe water: from late December 2017, more chlorine throughout the city's water system, 282 emergency chlorinated water tanks in the worst-hit neighborhoods — checked daily from January 15 — and household water treatment products for about 1 million households. Cases fell sharply in January.
• Vaccination: from January 10 to February 14, 2018, about 2 million doses of oral cholera vaccine — two doses each for about 1 million residents aged 1 and older, roughly 80% of the target group and half of Lusaka.
• Care and surveillance: training for about 100 health workers on detection and treatment; standard case definitions; daily reports; and door-to-door, mass media and community health worker outreach.

Why it came back

In mid-March 2018, a late rainy season brought heavy flooding, and emergency repairs at the city's main water treatment plant caused shortages. Flooded areas were full of pit latrines and shallow wells — ideal for contaminating drinking water — and cholera returned. Heavy rain has driven cholera outbreaks in Zambia and across Africa before.

Lessons

A fast, well-coordinated response, strong surveillance and a steady supply of chlorinated water can bring an outbreak under control. But cholera will keep coming back unless people have safe drinking water and sanitation. The Global Task Force on Cholera Control has proposed investing ahead of time in preparedness, water and sanitation, and oral vaccine where cholera spreads.

Sources

Based on Sinyange N, Brunkard JM, Kapata N, et al., "Cholera Epidemic — Lusaka, Zambia, October 2017–May 2018," MMWR Morbidity and Mortality Weekly Report, volume 67, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report's percentage of low-chlorine water sources with E. coli does not match its own counts, so it is not repeated here.