Strongyloides stercoralis infection in patients presenting with lower respiratory tract infections: a retrospective case series from a tertiary hospital in Vietnam

BACKGROUND: Strongyloides stercoralis infection is frequently overlooked in patients presenting with lower respiratory tract infections (LRTIs) because of nonspecific clinical manifestations, despite its potential to cause severe pulmonary involvement, particularly in endemic regions. METHODS: We conducted a retrospective case series at Bach Mai Hospital, a tertiary referral center in northern Vietnam. Adult patients hospitalized between January 2024 and July 2025 with LRTIs and confirmed S. stercoralis infection were included. Patients were classified as having chronic strongyloidiasis (including parasitologically confirmed and serology-only probable cases) or hyperinfection syndrome. Clinical, laboratory, radiological, microbiological, and diagnostic data were analyzed. RESULTS: A total of 42 patients were included (mean age 73.3 ± 10.2 years; 83.3% male). Among the 42 patients, 59.5% were classified as chronic strongyloidiasis, including both parasitologically confirmed and serology-only probable cases, whereas 40.5% had hyperinfection syndrome. In the hyperinfection group, respiratory involvement was more frequent than gastrointestinal involvement (58.8% vs. 41.2%). Pneumonia and acute exacerbations of chronic obstructive pulmonary disease were the predominant clinical presentations. Laboratory abnormalities were common, including hypoalbuminemia (88.1%), anemia (64.3%), and hyponatremia (50.0%), whereas eosinophilia was observed in only 23.8% of patients. Serological testing using ELISA showed the highest diagnostic yield (90.5%), while direct parasitological methods demonstrated limited sensitivity. Gram-negative enteric bacteria predominated among microbiological isolates. CONCLUSIONS: This retrospective case series characterizes the clinical and laboratory features of LRTIs in patients with concomitant S. stercoralis infection. Pneumonia and COPD exacerbations were predominant presentations, often with marked laboratory abnormalities despite infrequent eosinophilia. Although hyperinfection was frequent and direct parasitological tests showed limited sensitivity, no inference can be made regarding the frequency or strength of this association due to the descriptive design and lack of a comparator group. These findings may help clinicians consider strongyloidiasis in selected patients with unexplained or refractory LRTIs in endemic settings.