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First report of Karachi’s largest Dengue epidemic published by AKU

Daily Times Monitor

KARACHI: In the first report of the largest epidemic of dengue hemorrhagic fever (DHF) virus infection from Karachi, experts from the Aga Khan University Hospital found that adults were also susceptible and not just children as was previously believed.

These findings were presented in a study ‘Dengue outbreak in Karachi, Pakistan, 2006: experience at a tertiary care center’ by E. Khan, J. Siddiqui, S. Shakoor, V. Mehraj, B. Jamil and R. Hasan and was published online in the journal Transactions of the Royal Society of Tropical Medicine and Hygiene on Aug 13.

Medical records of 172 IgM-positive patients were reviewed. Patients were categorized into dengue fever (DF) and DHF. The mean age of the patients was 25.9 years, 55.8% were males. Five cases (2.9%) had a fatal outcome. Three were from a pediatric group (<15 years).

In Asia, dengue has made its route geographically from Southeast Asian countries. In India the first epidemic of dengue was reported in 1963–1964. Since then, multiple outbreaks have been reported from different regions of India. New Delhi has a record of seven outbreaks since 1967. The last major outbreak reported in Delhi was in 2003. In Pakistan the first confirmed outbreak of DHF was reported in 1994 by the AKUH; the serotype reported was DENV-2. Thereafter, sporadic cases of DHF continued to be documented from different parts of the country. Antibodies specific to DENV-1 and DENV-2 were found in sera of children presenting with undifferentiated fever in Karachi, indicating that these two dengue serotypes predominated/prevailed in the 1990s.

During 2005–2006, however, there was an unprecedented increase in epidemic DHF activity in the country, with a large number of cases being reported from Karachi. More than 3,640 patients with signs and symptoms suggestive of DF were admitted to several referral hospitals in the country, including the AKUH. There were 40 deaths, of which 37 were from the province of Sindh, making it the largest and most severe outbreak of DF in the country.

Between May and November 2006 a total of 3,075 serum samples were received for detection of anti-dengue IgM. Of these, 482 were from patients admitted with a clinical suspicion of DF or DHF, and 172 were found to be anti-dengue IgM-positive. The medical records of these 172 patients with confirmed laboratory diagnosis for dengue virus infection were reviewed retrospectively for demographic, clinical and laboratory data.

Most of the cases were from the east, center and north of Karachi. Two patients (1.2%) were referred from other parts of the Sindh province, while two patients were from Punjab. In 2006, the first case of DHF was admitted in the month of May. Thereafter, the numbers of cases steadily increased over the next 5 months. The largest number of cases was admitted from August to October, and the number of patients decreased during the month of November.

Unprecedented population growth and unplanned urbanization are the two main factors that have led to the emergence of dengue virus infection in tropical developing countries. Karachi is also facing a similar crisis.

Karachi experienced the first major outbreak of DHF in 1994, and since then DF has been recognized as one of the causes of fever in the area with few cases of DHF and very few deaths directly attributable to DHF/DSS. This is the first report of the largest epidemic of DHF with IgM-confirmed cases from Karachi, Pakistan.

Analysis of monthly dengue cases showed peak incidence from August to October 2006. DHF is considered primarily to be a disease of children under the age of 15 years and is a leading cause of hospitalization of young children in Southeast Asia. In the study, 83.6% of adult patients presented to the hospital with signs and symptoms compatible with DHF. A similar age distribution was also noted during the 1994–1995 outbreak in Karachi. This observation is consistent with reports from other endemic countries. A 3-year study from India showed a maximum number of cases between the ages of 21 and 30 years.

Hyperendemicity (co-circulation of more than one serotype) and/or introduction of a new virulent serotype in the community perhaps render the adult population more susceptible to a severe form of the disease. The population of Karachi has had a prior encounter with DENV-1 and 2. Serum samples from the patients with suspected DHF/DSS in the early part of this epidemic (autumn of 2005) revealed DENV-3 as the cause of the DHF.

The shift in the age distribution of DHF in the study population is consistent with observations in other studies conducted in other endemic regions and is perhaps due to the introduction of a new serotype of dengue (DENV-3) in Karachi.

The primary pathophysiologic abnormality seen in DHF and DSS is an acute increase in vascular permeability that leads to leakage of plasma into the extravascular compartments, resulting in hemoconcentration and decreased blood pressure. Plasma volume studies have shown a reduction of more than 20% in severe cases. In the study, hemoconcentration by definition was documented in a few patients only. This is a very important finding, as raised hematocrit is one of the defining characteristics of DHF, based on WHO criteria, and an elevated hematocrit value is used for case definition in field studies during outbreak situations. Iron deficiency anemia and hemoglobinopathies are major problems in Pakistan. About 5% of the Pakistani population carries the ?-thalassemia trait. The patients may have had a low baseline hematocrit, leading to relative hemoconcentration. The role of these factors leading to low hematocrit levels in the presence of DHF without overt hemorrhage in the study population needs further studies.

The experts observed a significant independent association of male gender and vomiting with DHF. It is their opinion that the uneven male-to-female ratio in the patient population is a reflection of the social bias of male gender in society. Failure to seek medical attention for females in the family (adults as well as children) in a timely manner may have led to high mortality in females.

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