Study on the Changes in Common Laboratory Parameters in Dengue Patients with Secondary Bacterial Infection

Secondary bacterial infection can adversely affect the clinical course of primary viral infection indengue fever. Time consuming microbiological culture confirmations and false negative culture resultsdelay the timely initiation of antibiotics. The objective of this study was to describe the variation in thecommon laboratory parameters during the illness, identify criteria that may predict secondary bacterialinfection before microbial culture confirmation, identify the common organisms causing secondarybacterial infections and their antibiotic sensitivity patterns. A retrospective case-control study was carriedout at the Dengue Management Unit of the National Institute of Infectious Diseases, Sri Lanka. Patientstreated with antibiotics upon suspicion or culture confirmation of secondary bacterial infections andpatients not treated with antibiotics were selected for the study. Total WBC count, absolute neutrophilcount, platelet count, HCT (Hematocrit), CRP (C Reactive Protein) and average body temperature wererecorded. Independent sample t-test was used to analyze the data. Study results showed that most positivemicrobial cultures were detected on the 6th and 7th days of illness. Staphylococcus, Streptococcus, andnon-speciated Gram-positive cocci were the commonly isolated organisms. Patients with confirmedsecondary bacterial infection had significantly higher neutrophil count (3.32±0.35x103/μL, p<0.05) andlower platelet counts (49.33±7.66x103/μL, p<0.05) on the 6th and 5th day of illness respectively. Theaverage body temperature was significantly higher in the study group than the control from the fever day3 onwards (p<0.05). The study subjects were more likely to have significantly lower HCT values(38.62±1.12%, p<0.05) than their controls on the third and fourth days of fever. Overall, the present studysuggests that bacterial co-infection increases the mortality rate in dengue patients. The variation inabsolute neutrophil count, platelet count, and body temperature pattern compared to the illness day can beused along for early prediction of secondary bacterial infection. 
Keywords:  dengue, bacterial infection, antibiotics, platelet count, HCT