According to newspaper reports 10 people recently died in Karachi of primary amoebic meningoencephalitis (PAM), caused by Naegleria fowleri. Naegleria fowleri is a heat-loving (thermophilic) microbe. It grows best at temperatures around 46°C and can survive for short periods at even higher temperatures. It is less likely to be found as temperatures decline.
N. fowleri causes an acute and hemorrhagic infection, (PAM), which is almost universally fatal. PAM occurs when water containing N. fowleri enters the nose, typically during swimming. N. fowleri migrates to the brain via the olfactory nerves, causing extensive damage to the frontal lobes of the brain. A sudden onset of bi-frontal headaches, high fever, stiff neck, nausea, vomiting, irritability and restlessness are the initial symptoms of PAM. Later, symptoms may include photophobia, diplopia, lethargy, confusion, bizarre behaviour, seizures and coma, preceding death. The disease progresses rapidly, and owing to the delay in making a correct diagnosis, the prognosis for the patient is poor. The striking feature of PAM is the rapid onset of symptoms following exposure to fresh water, within as little as 24 hours. The disease progresses rapidly and death usually occurs within a week or 10 days.
When evaluating potential sources of contaminated water associated with cases of PAM, it is important to understand that the route of infection is through the nose — PAM is not known to be caused by water ingestion. This point leads to the ablution that is performed before prayers. The best defence in this case is the presence of residual chlorine of the level of 0.5 mg/l (milligrams per litre). The Karachi water agency is asking mosques in Karachi to boil water for ablution; this is an impossible and impractical task.
According to reports, the residual chlorine content in most samples of the drinking water in Karachi is zero. In very few cases, the residual chlorine present ranged from 0.15 to 1.75 ppm (parts per million). This is much lower than the generally recommended level of residual chlorine of 0.5 mg/l (1 mg/l is 1 ppm).
Chlorination of drinking water in water treatment plants is not that simple. A number of parameters impact chlorine application. Chlorination will not be effective if the turbidity of water is more than three ntu (nephelometric turbidity units). This is because suspended particles protect micro organisms, which hide themselves within the particles to escape disinfection. Karachi drinking water is quite often turbid.
Disinfection process is also affected by the pH value of water. The optimum range of pH for chlorine disinfection is between 5.5 and 7.5. The effectiveness of chlorine disinfection reduces by a factor of between three and six when pH increases from six to nine. Chlorine disinfection is poor when pH is above nine.
Disinfection efficiency is significantly impacted by contact time. Contact time is defined as the period available for the interaction between the disinfectant and constituents in the water. The minimum contact time for chlorination is 30 minutes at 20°C to ensure effective disinfection. In case of Karachi, this means that there must be contact time of 30 minutes of chlorine with water, before the water reaches the first consumer. If the temperature drops below 20°C, the contact time should be increased.
The generally-accepted value of residual chlorine of 0.5 mg/l is required to be maintained in the distribution system up to the last customer. In Karachi, the water supply is intermittent and the water pipe systems leak. When the water supply is switched off, the pressure drops and the contaminated water enters the distribution system through the leaks in the pipes. The contamination that enters the pipelines will consume the residual chlorine and the net result will be zero residual chlorine further down the distribution system. The water agency in Karachi must note this point and undertake remedial measures.
The Karachi water agency has been asked to collect and analyse water samples for residual chlorine. This is not the correct approach. The most appropriate way is to ask a neutral and trust-worthy institution, like Aga Khan Hospital, to conduct such an analysis and make the results public. The Karachi water agency must provide residual chlorine of 0.5 mg/l throughout the water distribution system, up to the last consumer, if PAM infection is to be prevented.
Adding chlorine to water at household level (in addition to the chlorination done by the Karachi water agency) can be hazardous. If the residual chlorine level becomes greater than 0.5 mg/l, the chlorine will react with the organic matter present in the water and form trihalomethanes (chloroform, bromoform, bromodichloromethane, and dibromochloromethane). These are cancer-causing agents.
The best defence against N. fowleri at household level is the boiling of water. Once it comes to a boil, the water should be allowed to simmer for at least one minute (three minutes at 5,000 feet above mean sea-level) to ensure the bacteria is completely wiped out.