With this year's death toll from dengue infection crossing the 300-mark yesterday, the fatality rate has risen to 0.5 percent, mirroring the rates seen in 2020.

The fatality rate was 0.18 percent in 2019 when the hospitalisation cases hit an all-time high record of 1,01,354. The fatality rate was 0.37 percent in 2021 and 0.45 percent last year.

This year, the fatality rate among dengue patients in Dhaka is higher– 0.7 percent, while it is 0.2 percent outside Dhaka, according to the Directorate General of Health Services (DGHS).

The total number of fatalities this year rose to 303, including yesterday's 10, while the total number of hospitalised patients rose to 63,968 including yesterday's 2,495.

Experts, meanwhile, have cautioned that the fatality rate is likely to remain high due to the higher rate of second-time infection in different dengue serotypes/strains that led to severe illnesses quickly.

"Dengue virus has been causing infection among people in our country since 2000. As a result, more people are being infected for the second time with different dengue serotypes, leading to severe illness," Dr Khalilur Rahman, Director of Shaheed Shuhrawardy Medical College Hospital, told The Daily Star yesterday.

According to the researchers, there are four distinct serotypes of the dengue virus: DEN-1, DEN-2, DEN-3, and DEN-4.

These serotypes are closely related but differ slightly in their genetic makeup, leading to variations in their antigenic properties.

When a person is infected with one serotype of the dengue virus, they develop immunity to that specific serotype. However, this immunity does not provide protection against the other serotypes, according to researchers.

Different studies show that most people who are infected with dengue will have mild or no symptoms.

"This fact has left many dengue patients unaware that they have caught a subsequent infection with different serotypes. So, they develop severe illness fast, but come to hospital too late," Dr Khalilur Rahman said.

He said that coming to hospital late is also the main reason behind the higher death rate among young patients.

According to the DGHS, the fatality rate among patients aged 21-25 is the highest – around 11 percent; followed by 9 percent among patients aged 26-30; and 8 percent each among 31-40 and 56-60.

"So, our advice will be that patients come to the hospital before developing severe symptoms. And drastic fall of blood pressure is the major sign," he said.

According to the World Health Organisation (WHO), severe dengue symptoms often come after the fever has gone away.

According to physicians, there are seven symptoms of severe dengue: intolerable abdominal pain, persistent vomiting, breathing difficulty, bleeding gums or nose, slurred speech, declining blood pressure and severe fatigue which leaves a patient unable to even walk or stand up.

Different studies show that most people who are infected with dengue will have mild or no symptoms.

But for those who do, the most common symptoms are high fever, headache, body ache, nausea and rash and most get better in 1-2 weeks, according to the WHO.

Prof Dr Saif Ullah Munshi, a virologist at Bangbandhu Sheikh Mujib Medical University, said that the four-five days following the patient's report of "no fever" are crucial.

"This is because patients may go into shock (or may develop severe symptoms) at any time during this period. So, taking caution is crucial at this time," Prof Saif Ullah Munshi told The Daily Star earlier.

According to different studies, the mortality rate among patients with severe symptoms is 1 percent if treated. When untreated, the mortality rate is 5 percent.

This year, the number of dengue cases started surging early on due to weak mosquito containment efforts and other relevant factors, leaving the hospitals under pressure.

As of yesterday morning, a total of 9,334 dengue patients were undergoing treatment at different hospitals countrywide, which is around 15 percent of all dengue cases this year.