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 in dengue fever. Time consuming microbiological culture confirmations and false negative culture results delay the timely initiation of antibiotics. The objective of this study was to describe the variation in the common laboratory parameters during the illness, identify criteria that may predict secondary bacterial infection before microbial culture confirmation, identify the common organisms causing secondary bacterial infections and their antibiotic sensitivity patterns. A retrospective case-control study was carried out at the Dengue Management Unit of the National Institute of Infectious Diseases, Sri Lanka. Patients treated with antibiotics upon suspicion or culture confirmation of secondary bacterial infections and patients not treated with antibiotics were selected for the study. Total WBC count, absolute neutrophil count, platelet count, HCT (Hematocrit), CRP (C Reactive Protein) and average body temperature were recorded. Independent sample t-test was used to analyze the data. Study results showed that most positive microbial cultures were detected on the 6th and 7th days of illness. Staphylococcus, Streptococcus, and non-speciated Gram-positive cocci were the commonly isolated organisms. Patients with confirmed secondary bacterial infection had significantly higher neutrophil count (3.32±0.35x103/μL, p<0.05) and lower platelet counts (49.33±7.66x103/μL, p<0.05) on the 6th and 5th day of illness respectively. The average body temperature was significantly higher in the study group than the control from the fever day 3 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 study suggests that bacterial co-infection increases the mortality rate in dengue patients. The variation in absolute neutrophil count, platelet count, and body temperature pattern compared to the illness day can be used along for early prediction of secondary bacterial infection. Keywords:  dengue, bacterial infection, antibiotics, platelet count, HC