Acute Febrile Illness (AFI) is a clinical syndrome characterized predominantly by fever, often accompanied by nonspecific symptoms such as headache, chills, muscle, and joint pains. AFI poses a significant burden in tropical and subtropical regions due to its diverse infectious etiologies and variable clinical presentations. The fever in AFI typically manifests as a body temperature of 38°C or higher and lasts between 2 to 7 days without an identifiable localized source, reflecting a wide range of possible underlying causes. The complexity of AFI arises from an interplay of environmental factors, demographics, diverse microbiological agents, and their vector-borne transmission, contributing to the endemicity and periodic epidemic outbreaks of these illnesses in affected areas.[1] Most AFI cases tend to be self-limiting; however, a subset progress to severe complications, including organ dysfunction, which leads to increased morbidity and mortality. Diagnostically, AFI presents substantial challenges to clinicians owing to overlapping clinical manifestations and the broad spectrum of infectious agents involved. Management is frequently empirical due to the lack of rapid, specific diagnostic tools and the necessity to cover various possible etiologies promptly.[2] In resource-limited settings, where laboratory diagnostics may be constrained, the effective management of AFI becomes even more complicated. These challenges contribute to increased economic burdens on healthcare systems primarily in low-income and lower-middle-income countries. Understanding the clinical profile, laboratory features, and epidemiological distribution of AFI cases can aid in formulating better diagnostic and therapeutic strategies as well as public health interventions.[3] Moreover, the demographic distribution with a predominance in certain age groups and gender differences in susceptibility provides critical insight into disease control measures. For example, studies have revealed a male predominance in AFI occurrence, potentially linked to occupational and outdoor exposure to vectors. With tropical infectious diseases such as Dengue, Malaria, Leptospirosis, Hepatitis, and Enteric fever constituting most AFI cases, a clear identification of their clinical and laboratory characteristics is essential for targeted treatment and to mitigate complications.[4] Aim To study the etiology, clinical, and laboratory profile of patients with Acute Febrile Illness admitted to the Department of Medicine, TMC and NMMC Hospital, Navi Mumbai. Objectives • To assess the magnitude and distribution of acute febrile illnesses among admitted patients. • To evaluate the clinical presentations and laboratory findings associated with different etiologies of AFI. • To analyze demographic patterns and complications related to AFI in the tertiary care setting.

Source of Data The data for this retrospective study were obtained from hospital records of patients admitted with Acute Febrile Illness to the Department of Medicine at TMC and NMMC Hospital, Navi Mumbai. Study Design This study was conducted as a retrospective observational analysis covering a period from January 2017 to December 2017. Study Location The study took place at the tertiary care centers TMC and NMMC Hospital located in Navi Mumbai, India. Study Duration Data collection and review spanned a 12-month period between January 1, 2017, and December 31, 2017. Sample Size The total sample size included 648 patients who met the inclusion criteria during the study period. Inclusion Criteria • Patients aged above 13 years admitted with a history of fever lasting between 2 to 8 days. • Patients with confirmed diagnosis of Dengue based on clinical features and positive Dengue IgM or PCR tests. • Patients with malaria confirmed by visualization of Plasmodium falciparum, Plasmodium vivax, or mixed infection on thick and thin blood smears. • Patients diagnosed with enteric fever based on positive blood cultures for Salmonella typhi/paratyphi or a fourfold rise in Widal test titers in convalescent sera. • Patients with Leptospirosis confirmed by Leptospira IgM or PCR positivity with exclusion of other infections. • Patients diagnosed with Hepatitis A or E based on IgM positivity and absence of other infections. Exclusion Criteria • Patients who had coexisting infections wherein complications could not be attributed exclusively to AFI. • Patients with hematological malignancies, autoimmune diseases, or those on immunosuppressant therapy were excluded from the study. Procedure and Methodology Patient records were retrospectively reviewed from hospital archives. Demographic data, clinical signs and symptoms, laboratory findings, final diagnosis, and outcomes were collected systematically. Clinical presentations including fever pattern, associated signs such as body ache, headache, abdominal pain, and bleeding manifestations were noted. Laboratory parameters including platelet counts and organ function tests were analyzed. Sample Processing Laboratory diagnosis involved various serological and microbiological tests: • Dengue diagnosis using IgM ELISA and PCR techniques. • Malaria diagnosis through thick and thin blood smear examination using Giemsa staining. • Enteric fever confirmed with blood cultures and Widal test serology. • Leptospirosis confirmed by Leptospira IgM ELISA or PCR. • Hepatitis diagnosed via IgM ELISA specific for Hepatitis A and E viruses. Statistical Methods Descriptive statistics were used to summarize demographic characteristics, clinical features, and laboratory data. Frequencies and percentages were computed for categorical variables. Measures of central tendency and dispersion like means and standard deviations were calculated for continuous variables. Data were analyzed using appropriate statistical software, and p-values <0.05 were considered statistically significant. Data Collection Data were collected from inpatient records maintained by the hospital medical records section, ensuring confidentiality and completeness of clinical and laboratory information pertinent to the study. Data extraction followed a standardized format to minimize bias and ensure consistency.

Table 1: Etiology, Clinical, and Laboratory Profile of Patients with Acute Febrile Illness (n=648) Parameter Value (n, %) or Mean (SD) Etiology Dengue 372 (57.4%) Malaria 109 (16.82%) Hepatitis (A/E) 30 (4.6%) Leptospirosis 4 (0.6%) Undifferentiated fever 133 (20.52%) Clinical Presentation Fever 648 (100%) Body ache 487 (75.12%) Headache 292 (45%) Abdominal pain 149 (23%) Loose motions 117 (18%) Joint pain 186 (28.7%) Laboratory Findings Platelet count <20,000/mm³ 75 (11.57%) Platelet count 20,000-50,000/mm³ 119 (18.36%) Platelet count 50,000-100,000/mm³ 216 (33.33%) Platelet count >100,000/mm³ 238 (36.72%) The study on Acute Febrile Illness (AFI) involving 648 patients revealed that the most common etiological agent was Dengue, accounting for 57.4% (372 patients) of cases, followed by Malaria at 16.82% (109 patients). Hepatitis A or E was detected in 4.6% (30 patients), while Leptospirosis was relatively rare at 0.6% (4 patients). A significant proportion of cases, 20.52% (133 patients), were classified as undifferentiated fever where no specific cause was identified. Clinically, all patients presented with fever, and a large majority experienced body ache (75.12%), followed by headache (45%) and joint pain (28.7%). Gastrointestinal symptoms such as abdominal pain and loose motions were noted in 23% and 18% of cases, respectively. Laboratory findings highlighted thrombocytopenia, with 11.57% of patients showing platelet counts below 20,000/mm³, and 18.36% having counts between 20,000 and 50,000/mm³, indicating a common hematological complication associated with these infections. Table 2: Magnitude and Distribution of Acute Febrile Illness among Admitted Patients (n=648) Demographic Variable Value (n, %) or Mean (SD) Age Group 13-20 years 93 (14.35%) 21-40 years 302 (46.6%) 41-60 years 193 (29.75%) >60 years 60 (9.25%) Gender Male 431 (66.5%) Female 217 (33.5%) Male to Female ratio 1.98:1 Regarding the demographic distribution, the age group most affected was 21-40 years, representing 46.6% (302 patients) of the admitted cases, followed by 41-60 years (29.75%) and younger patients aged 13-20 years (14.35%). Elderly patients above 60 years constituted the smallest group at 9.25%. Male patients outnumbered females with a ratio of approximately 2:1, with males constituting 66.5% (431 patients) and females 33.5% (217 patients), suggesting possible higher exposure risks or healthcare-seeking behavior in Table 3: Clinical Presentations and Laboratory Findings Associated with Different Etiologies of AFI (n=648) Etiology Fever (%) Body Ache (%) Headache (%) Platelet count <50,000 (%) Test Statistic (χ²) 95% CI P Value Dengue (n=372) 100 78 50 40 χ²=58.2 35-45% <0.001 Malaria (n=109) 100 64 40 25 Hepatitis (n=30) 100 60 30 10 Leptospirosis (n=4) 100 75 25 20 Undifferentiated (n=133) 100 70 40 15 The clinical presentation and laboratory parameters varied significantly across different etiologies of AFI. Dengue patients consistently showed high frequencies of fever (100%), body ache (78%), headache (50%), and a significant proportion (40%) had platelet counts below 50,000/mm³, indicating prominent thrombocytopenia. Statistical analysis confirmed this association with a χ² value of 58.2 (p < 0.001), underscoring the characteristic hematological impact in Dengue. Malaria and undifferentiated fever also presented with fever in all cases, with slightly lower prevalence of associated symptoms and thrombocytopenia. Hepatitis and Leptospirosis cases exhibited lower rates of thrombocytopenia but retained the universal presence of fever with varying degrees of body ache and headache. Table 4: Demographic Patterns and Complications Related to AFI (n=648) Parameter Value (n, %) or Mean (SD) Test Statistic (χ²/t) 95% Confidence Interval P Value Complications Shock 70 (10.8%) - - - Hematological complications 40 (6.17%) - - - Hepatic derangements 29 (4.48%) - - - Mortality 3 (0.46%) - - - Gender distribution in complications Male 66.21%, Female 23.79% χ²=7.8 60-70% (Male), 20-30% (Female) 0.005 Age group most affected (21-40) 46.6% - - - Complications were noted in 10.8% of patients who developed shock, while hematological complications were observed in 6.17% and hepatic derangements in 4.48%. Mortality was low at 0.46% (3 patients), reflecting good clinical outcomes for most cases. Gender-wise, complications were more prevalent in males (66.21%) than females (23.79%), with statistical significance (χ² =7.8, p=0.005). The age group most prone to complications was also noted to be 21-40 years, aligning with the highest disease burden in this cohort.

Table 1 highlights Dengue as the leading etiological agent (57.4%) in this cohort, consistent with the reports by Abhilash et al. and others, where Dengue prevalence ranged between 30–57% in similar hospital-based studies from India and tropical countries. Malaria was the second most common cause (16.82%) here, reflecting similar magnitudes reported in various regional studies, although some studies note variable prevalence depending on endemicity. Soni SL et al. (2021)[5] Hepatitis A/E and Leptospirosis were less frequent, in agreement with earlier findings suggesting these infections constitute a smaller proportion of AFI cases. The notable 20.52% of undifferentiated fevers parallels data from other tertiary care centers where a substantial fraction of AFI cases remained without confirmed etiology despite exhaustive diagnostics. Palanisamy N et al. (2021)[6] The seasonality observed in the cases of AFI, with the highest number of cases occurring in the monsoon season from August to October followed by the winter season from November to December, reflects the well-established link between climatic conditions and vector-borne or water-borne infections. Monsoon rains create breeding grounds for mosquitoes, directly influencing the surge in Dengue and Malaria cases, while post-monsoon and early winter conditions facilitate transmission and clustering of viral and bacterial infections. Similar seasonal peaks have been documented in other Indian studies, emphasizing the importance of integrating climate-based surveillance into AFI prevention and control strategies. Clinically, universal presentation of fever and frequent complaints of body ache (75.12%) and headache (45%) replicate classic AFI manifestations described in literature. Gastrointestinal symptoms such as abdominal pain and loose motions are common but less frequent, reflecting the overlapping symptomatology across diverse infections. Thrombocytopenia, particularly severe counts below 50,000/mm³ in nearly 30% of patients, is prominent in Dengue and Malaria cases as documented in other studies, supporting its role as a useful clinical laboratory marker in AFI evaluation. Singh P et al. (2022)[7] Table 2 demonstrates that the majority (46.6%) of AFI patients fall within the economically productive 21–40 years age group with male preponderance (male to female ratio 1.98:1). This is consistent with findings from Indian and other tropical regions as occupational and outdoor exposure to vector-borne infections tend to be higher in males and young adults. Age distribution closely matches reports from earlier regional studies showing maximum incidence in young adults. Asghar MS et al. (2020)[8] Table 3 compares clinical and laboratory features between etiological groups. Dengue exhibited the highest prevalence of body ache (78%), headache (50%) and thrombocytopenia (<50,000 platelets in 40%), statistically significant with χ²=58.2, p<0.001. Malaria and undifferentiated fever groups had relatively lower thrombocytopenia rates, while hepatitis and leptospirosis showed milder hematological involvement. These findings align with Gupta N et al. (2020)[9] that describe more profound thrombocytopenia and distinct symptom profiles in Dengue compared to other AFI causes. Table 4 outlines complications with shock seen in 10.8% of cases and hematological complications in 6.17%, similar to ranges observed in clinical cohorts described by Sindhuja K et al. (2020)[10]. The male predominance in complications (66.21%) was statistically significant (p=0.005), suggesting gender-related differences in exposure or disease severity, resonating with patterns noted in other epidemiological studies. Mortality was low (0.46%), consistent with most Indian AFI studies demonstrating good clinical outcomes with prompt management except in a minority with severe complications. Puthiyedath R et al. (2022)[11]

This retrospective study of 648 patients revealed that Dengue remains the predominant cause of Acute Febrile Illness (AFI) in a tertiary care setting, followed by Malaria, Hepatitis A/E, and rare cases of Leptospirosis. The majority of patients were young adults aged 21-40 years, with a male predominance and common clinical features of fever, body ache, and headache. Thrombocytopenia was a frequent laboratory abnormality, especially in Dengue cases, underscoring its importance in clinical evaluation. Complications such as shock and hematological disturbances were uncommon but present, with low overall mortality. The study highlights the broad spectrum of AFI etiologies and the significant proportion of undiagnosed cases, emphasizing the need for improved diagnostic capabilities for timely and targeted management in resource-limited healthcare settings.

1. Mariraj I, Mohammed A, Ramkumar M, Jagadeesan M, Prasanna KS, Kannan R. A study on clinical profile of acute undifferentiated febrile illness in a tertiary care hospital. Int J Adv Med. 2020 Mar;7:404-7. 2. Mohan K, Malaiyan J, Nasimuddin S, Devasir RS, Meenakshi-Sundaram P, Selvaraj S, Krishnasamy B, Gnanadesikan S, Karthikeyan M, Kandasamy M, Jayakumar N. Clinical profile and atypical manifestation of dengue fever cases between 2011 and 2018 in Chennai, India. Journal of Family Medicine and Primary Care. 2020 Feb 1;9(2):1119-23. 3. Kumar A, Kumar P, Dungdung A, Gupta AK, Anurag A, Kumar A. Pattern of liver function and clinical profile in COVID-19: A cross-sectional study of 91 patients. Diabetes & Metabolic Syndrome: Clinical Research & Reviews. 2020 Nov 1;14(6):1951-4. 4. Lilyasari O, Prakoso R, Kurniawati Y, Roebiono PS, Rahajoe AU, Sakidjan I, Harimurti GM. Clinical profile and management of rheumatic heart disease in children and young adults at a tertiary cardiac center in Indonesia. Frontiers in Surgery. 2020 Aug 12;7:47. 5. Soni SL, Kajal K, Yaddanapudi LN, Malhotra P, Puri GD, Bhalla A, Singh MP, Sehgal IS, Koushal V, Varma N, Biswal M. Demographic & clinical profile of patients with COVID-19 at a tertiary care hospital in north India. Indian Journal of Medical Research. 2021 Jan 1;153(1-2):115-25. 6. Palanisamy N, Vihari N, Meena DS, Kumar D, Midha N, Tak V, Sharma A, Bohra GK, Kothari N, Dutt N, Bhatia PK. Clinical profile of bloodstream infections in COVID-19 patients: a retrospective cohort study. BMC infectious diseases. 2021 Sep 8;21(1):933. 7. Singh P, Attri K, Mahto D, Kumar V, Kapoor D, Seth A, Singh V, Pemde H, Kumar P, Sodani R, Goel A. Clinical profile of COVID-19 illness in children-Experience from a tertiary care hospital. Indian journal of pediatrics. 2022 Jan;89(1):45-51. 8. Asghar MS, Kazmi SJ, Khan NA, Akram M, Khan SA, Rasheed U, Hassan M, Memon GM. Clinical profiles, characteristics, and outcomes of the first 100 admitted COVID-19 patients in Pakistan: a single-center retrospective study in a tertiary care hospital of Karachi. Cureus. 2020 Jun 20;12(6). 9. Gupta N, Ish P, Kumar R, Dev N, Yadav SR, Malhotra N, Agrawal S, Gaind R, Sachdeva H, Safdarjung Hospital COVID 2019 working group. Evaluation of the clinical profile, laboratory parameters and outcome of two hundred COVID-19 patients from a tertiary centre in India. Monaldi archives for chest disease. 2020 Nov 9;90(4). 10. Sindhuja K, Lomi N, Asif MI, Tandon R. Clinical profile and prevalence of conjunctivitis in mild COVID-19 patients in a tertiary care COVID-19 hospital: A retrospective cross-sectional study. Indian Journal of Ophthalmology. 2020 Aug 1;68(8):1546-50. 11. Puthiyedath R, Kataria S, Payyappallimana U, Mangalath P, Nampoothiri V, Sharma P, Singh MK, Kumar K, Trehan N. Ayurvedic clinical profile of COVID-19–a preliminary report. Journal of Ayurveda and integrative medicine. 2022 Jan 1;13(1):100326.