A WHO report last year had warned Bangladesh against a potentially severe dengue outbreak anytime.

Since the onset of dengue infection in the city in early May this year, four persons have been hospitalised, three in Dhaka Shishu Hospital and one in Dhaka Medical College Hospital, sources at the Directorate of Health said yesterday.

Unofficially, at least 15 people have been hospitalised so far in different private clinics. Three of them are now said to be in critical condition.

Doctors in most government hospitals and private clinics said most of the infected patients are wrongly diagnosed for common jaundice or typhoid. "This is even more dangerous since the strong antibiotics harmfully interact with the dengue virus," said one doctor.

Some experts, requesting anonymity, have warned that the early sporadic rains in the city this year created a perfect breeding environment for the Aedes mosquitoes that carry the deadly virus.

But despite warnings, the agencies concerned have not yet issued any warning against a possible dengue epidemic in the city, they said.

In retrospect, when some cases of dengue were reported in the city's Hatirpool, Mirpur and Jhikatola areas in 1999, health directorate officials brushed it aside as 'scattered incidents posing no threat to the population.'

Expert like Touhid Uddin Ahmed, former chief scientific officer of Institute of Epidemiology, Disease Control and Research (IEDCR) had then warned the government of possible dengue infection in Bangladesh considering its existence in neighbouring countries.

About a year later in July 2000, when Dengue Haemorrhagic Fever (DHF) started claiming lives, the Dhaka City Corporation (DCC) Mayor Mohammad Hanif still believed that the dengue virus was 'being imported' from neighbouring countries.

Last year, 93 people died out of over 5500 infected, mostly in municipal areas across the country, according to official statistics.

Due to lack of diagnostic facilities, a large number of dengue fever cases in the country went undetected in the past, experts said. In fact, many people who were earlier said to have died from common viral infection are now believed to have died from DHF that leads to bleeding.

Studies by IEDCR and Armed Forces Research Institute of Medical Sciences concluded last year that mixed infection in the blood of two or more of the four types of dengue viruses caused DHF.

A WHO report on dengue situation since 1995 said that a high percentage of population in Dhaka and Chittagong has antibodies in their blood to fight dengue infection type - 3 and to a lesser extent, types 1 and 2.

The report also said that in 1996 in Myanmar, 2,243 out of 83,381 recorded cases of dengue infection were fatal. In the same year in India, a fifth of more than 9,000 infected people died.

The growth of Aedes mosquito population is measured by the percentage of containers placed in houses that are found with Aedes larvae. This measurement is known as the Breteau index and an index of up to 18 is considered normal.

A 1997 survey showed that the index had reached 30 in the city. It rose further to 160 in 1999 and to a shocking 254 in June 2000. But the DCC and the health ministry ignored experts' warnings about a dengue outbreak.

WHO currently estimates the annual global incidence of the disease to be 50 million. An estimated 2500 million people in the world, two-fifths of its population, are at risk of dengue infection.

Before 1970, cases of DHF were reported in nine countries only. The number increased by four times by 1995.

In 1998 alone, there were more than 616,000 cases in the Americas, mostly children under fifteen, of which 11,000 were cases of DHF.

The latest WHO report on 'Dengue and Dengue Haemorrhagic Fever' also said, not only the number of cases are increasing as the disease is spreading to new areas but explosive outbreaks are also occurring.

In Brazil, the number of reported cases in 1998 was 475,000 - more than the total number of cases in the continent in the previous year.

An estimated 500,000 infected people are hospitalised each year and roughly five per cent of the patients die.

According to the WHO report, most seriously affected areas are the Southeast and Western Pacific regions.

Experts say strict environmental management coupled with spraying of insecticides is essential to control the Aedes mosquito population.

They say proper solid waste disposal and improved water storage practices, including covering containers to prevent access of egg-laying female mosquitoes are some of the methods that should be encouraged through community-based programmes.

The application of appropriate insecticides to larvae or eggs prevents mosquito from breeding for several weeks but the process should be repeated periodically.