Health Stream Literature Summary - Issue 33 March 2004 - Bonus article

An outbreak of Vibrio cholerae 01 infections on Ebeye Island, Republic of the Marshall Islands, associated with use of adequately chlorinated water source.
Beatty ME, Jack T, Sivapalasingam S, Yao SS, Paul I, Bibb B, Greene KD, Kubota K, Mintz ED, Brooks JT. Clin Infect Dis 2004 38:1-9

On the Island of Ebeye in the Republic of the Marshall Islands a sudden increase in the number of acute, severely dehydrating cases of diarrhoeal illness occurred among adults during early December 2000. A similar increase in diarrhoeal illness was also reported shortly after on Lae Island, in Lae Atoll, 100 miles away. Stool specimens from these islands were tested and Vibrio cholerae 01, biotype El Tor, serotype Ogawa was found, indicating a cholera outbreak. To investigate the risk factors for developing cholera a case-control study was undertaken in Ebeye.

Case patients were identified from patients presenting to Ebeye Hospital between 1 December 2000 and 6 January 2001. Case were defined as those with acute onset of watery or nonbloody diarrhoea over 5 years of age. Attack rates were calculated by administrative zone using the 1999 census data. An index case was the first person in their household with cholera. Each index case was matched randomly to 2 control subjects by age, sex and neighbourhood of residence. Controls were excluded if they had not resided on Ebeye during all 5 days before the onset of diarrhoea in their matched case or if anyone in their household reported diarrhoea in the month before the case's diarrhoea onset, or if they had received a cholera vaccination, or had declined to provide a blood sample.

As there are no fresh water springs in Ebeye, chlorinated water from the US military facility on the neighbouring island of Kwajalein is transported by individuals, often children, in containers via a ferry to Ebeye. The chlorine concentration was measured in water samples from this source. Samples of three powdered drink mixes consumed by those on Ebeye during the outbreak period were collected and reconstituted with distilled water and tested.

There were 53 index case patients in the study and 104 controls. Case patients had significantly higher odds of having collected their main source of drinking water from the Kwajalein military base during the 5 days prior to onset of diarrhoea and had significantly lower odds of having consumed mainly rainwater. Case patients also had significantly higher odds of having used any water from the Kwajalein military base in the 5 days before illness than controls and significantly lower odds of having used any bottled water or any rainwater.

Reduced odds of illness were associated with using an insulated water cooler with a spout to either transport of store water from Kwajalein. Reduced odds of illness were also associated with using a spout to transfer or remove drinking water from a container. Drinking boiled water, drinking water flavoured with powdered drink mixes, consumption of fruits and vegetables, eggs, beef, salt fish, crab and pancakes, and having heard a radio program about cholera were all associated with reduced odds of illness.

Chlorine levels in the Kwajalein military base water source were found to be adequate (mean 2.1 mg//L, range 0.8 - 3.2 mg/L), and it was concluded that the cause of the oubreak was most likely contamination of water during transport and use. Sanitation in Ebeye is poor with no functioning sewage treatment plant since 1996 and raw sewage overflows into the streets during storms.

This was the first known outbreak of cholera in the Republic of the Marshall Islands. About 1% of the population was affected and six deaths were recorded among 103 patients meeting the case definition for cholera. This outbreak showed that a safe water source may not be adequate to prevent transmission of cholera and that contamination of water can occur if drinking water is not handled and stored safely.

Comment The title of this paper seems misleading as the water source does appear to have been adequately chlorinated - contamination appears to have occurred during transport and/or storage of the water.