When 30-year-old Tabarigum walked into Apollo Hospital in Jasola on August 18, he was expecting a routine check-up after chemotherapy. A bone-marrow biopsy showed no evidence of leukaemia — an encouraging sign that his treatment was working. But tests for his respiratory symptoms came back positive for H1N1 influenza, commonly known as swine flu, just as cases of the infection were climbing sharply across Delhi.The timing was particularly worrying because Tabarigum’s immune system had been severely weakened by chemotherapy.Delhi has recorded 1,777 H1N1 cases this year, according to health department data, with 114 fresh cases reported on August 20 alone. The capital has recorded 2,392 Influenza-A infections overall, prompting health authorities to review hospital preparedness and issue advisories on prevention and early treatment.For someone undergoing cancer treatment, however, the numbers are more than a public health statistic. They can translate into a much higher risk from what might otherwise look like an ordinary seasonal infection.Also Read | Cancer therapy breakthrough: Vaccine cuts skin cancer recurrence risk in landmark trial‘I could not even complete a sentence’Tabarigum, who grew up in Doimukh, Arunachal Pradesh, was diagnosed with acute myeloid leukaemia (AML), an aggressive blood cancer that begins in the bone marrow, earlier this year while preparing to donate blood to his mother, who was being treated for ovarian cancer. He was started on induction chemotherapy — an intensive first phase of treatment designed to eliminate as many leukaemia cells as possible and push the disease into remission.Chemotherapy can suppress the body’s ability to fight infections, particularly when white blood cell and neutrophil counts fall sharply. That makes respiratory viruses such as influenza a greater concern for patients receiving cancer treatment. Immunocompromised people are recognised as a high-risk group for severe influenza complications.In August, Tabarigum developed what initially sounded like a routine respiratory illness — a cold and runny nose followed by high fever and a cough. Then the cough became relentless. “I could not even complete a sentence without coughing; it was so bad,” he says.Story continues below this adAlso Read | Over 80% of India’s elderly could face dangerous heat stress at 3°C global warming, says Lancet studyThe infection was the new threatWhen Tabarigum reached Apollo Hospital on August 18, his doctors found that his total leukocyte count and absolute neutrophil count were very low.“When we admitted Tabarigum, he had high-grade fever,” says Dr Chatterjee, an internal medicine specialist at Apollo Hospital, who treated him. “He was undergoing chemotherapy, which had significantly suppressed his immunity. Though he required minimal oxygen support, he was kept in an isolation room for five days. Now, he is fully recovered.”For Tabarigum, the immediate challenge had shifted from treating cancer to ensuring that a viral respiratory infection did not spiral into a severe complication. That is the larger concern doctors are flagging as Delhi’s H1N1 cases spiral.Why immunocompromised patients need to be more watchfulFor most healthy people, H1N1 may cause a flu-like illness with fever, cough, sore throat, body aches and fatigue. But the risk profile changes when the body’s immune defences are already compromised. People undergoing chemotherapy, those with certain cancers, transplant recipients and others with weakened immunity can have a greater risk of severe influenza, including pneumonia and hospitalisation.Story continues below this adDr Chatterjee says the concern is particularly high among patients who already have other health problems. “For those with co-morbidities such as diabetes, chronic heart or lung disease, the elderly, and immunosuppressed patients undergoing cancer treatment, swine flu carries the risk of respiratory failure and secondary infection leading to multi-organ dysfunction,” he says.A fever, cough or sudden worsening of breathing during chemotherapy should prompt contact with the treating medical team rather than waiting for symptoms to become severe. “Early assessment can help doctors decide whether influenza testing, antiviral treatment or hospital care is needed,” says Dr Chatterjee.India’s National Centre for Disease Control continues to maintain technical guidance on seasonal influenza, including H1N1, covering patient categorisation, home care, masks, clinical protocols and vaccination.The importance of acting earlyDr Chatterjee says antiviral treatment with oseltamivir can be useful when started early, while vaccination remains an important preventive measure for eligible people. “It’s a virus which is preventable with a vaccine shot,” he says.Story continues below this adVaccination decisions for people undergoing chemotherapy or otherwise immunocompromised should, however, be made in consultation with their treating doctor, because the immune response to vaccination can be reduced during some cancer treatments and the timing may need to be considered. For families caring for someone with suppressed immunity, prevention also becomes a collective responsibility: avoiding close contact with people who are unwell, maintaining hand and respiratory hygiene, using masks in crowded or high-risk settings when advised, and seeking medical advice promptly when symptoms appear.Back home, with one battle behind himTabarigum has now recovered and has been discharged from hospital. He is on his way back to Arunachal Pradesh. His experience also illustrates why Delhi’s current H1N1 surge deserves particular attention from people whose immune systems have been weakened by cancer or its treatment. For them, the warning signs may begin like they do for everyone else: a fever, a cough, a runny nose. “But they have far less room to wait and watch,” adds Dr Chatterjee.