With the rising incidence of cancer in low and lower-middle-income countries, the burden of pneumonia, which causes disproportionate morbidity and mortality in cancer patients, presents an evidence gap.

We conducted a 1-year prospective cohort study in the oncology ICU at Tata Medical Center Kolkata, to determine the incidence, risk factors, etiology and impact of pneumonia on length of stay and mortality. Pneumonia was identified via daily ICU rounds using clinical and radiological features. A 1:1 age and sex matched comparison cohort without pneumonia was included. Etiology of pneumonia was determined using microscopy, culture, ELISA, PCR and cartridge-based nucleic acid amplification tests. Logistic regression was used to study risk factors, Cox regression for mortality and linear regression for hospital and ICU length of stay.

There were 2279 ICU admissions. We recruited 711 patients: 355 had pneumonia, 356 did not. The incidence of pneumonia was 15.6% (95% CI: 14.1%–17.1%); 51.8% were community-acquired (CAP) and 48.2% were hospital-acquired (HAP). Seventy percent of CAP patients experienced recent healthcare exposure, with 28% hospitalised.

All-cause 90-day mortality (6.4 per 1000 person-days) was 9 times higher in pneumonia patients. Lengths of hospital stay (18.6 days), ICU stay (10.9 days) and mechanical ventilation (2 days) were higher in pneumonia patients.

Seventy-three percent of pneumonia patients had positive microbiology from lower respiratory samples. Gram-negative bacilli were frequent in both CAP and HAP. Influenza A/B was frequent in the monsoon and Haemophilus influenzae in the winter.

Bone-marrow transplant, hematological malignancies, neutropenia and chronic obstructive pulmonary disease increased pneumonia risk. CAP, h ematological malignancies and neutropenia increased the risk of death by day 90.

Pneumonia, both CAP and HAP, increased mortality and hospital and ICU length of stay in adults with cancer. Gram-negative bacilli were common in both CAP and HAP. Tailored infection control programmes and an emphasis on adult vaccination are imperative to pneumonia prevention.