Cytomegalovirus (CMV) is a major cause of congenital infection and morbidity in immunocompromised patients; CMV pneumonia remains rare in immunocompetent infants and should raise suspicion of an underlying immune deficiency. We report the case of an 11-month-old infant, with no relevant past medical history, admitted for febrile respiratory distress complicating a chronic respira- tory disorder evolving over two months, previously misdiagnosed and treated as pneumonia and then as infantile asthma. Chest radiography and computed tomography showed bilateral interstitial infiltrates with absence of the thymic shadow. Because of the lack of improvement under empirical antibiotic therapy, positive CMV serology and blood PCR led to treatment with Ganciclovir, with marked clinical improvement. Immunological work-up revealed hypogammaglobulinemia and a lymphocyte immunophenotyping pattern consistent with severe combined immunodeficiency (low CD19 B-cells and CD4 T-cells, normal NK cells). Cotrimoxazole antibiotic prophylaxis and immunoglobulin replacement therapy were started. CMV infection should be investigated in any infant presenting with atypical, chronic, or treatment-resistant interstitial pneumonia, and its identification should systematically prompt screening for an underlying primary immunodeficiency, the early diagnosis of which determines prognosis.

Keywords: Cytomegalovirus; Pneumonia; Severe Combined Immunodeficiency; Infant; Primary Immunodeficiency; Ganciclovir

1. Ong DSY., et al. “Comparative clinical manifestations and immune effects of cytomegalovirus infections following distinct types of immunosuppression”. Clinical Microbiology and Infection10 (2022): 1335-1344.
2. Rafailidis PI., et al. “Severe cytomegalovirus infection in apparently immunocompetent patients”. Virology Journal 5 (2008): 47.
3. Russell MY., et al. “Cytomegalovirus infection in pediatric immunocompromised hosts”. Infectious Disorders - Drug Targets5 (2011): 437-448.
4. Fernández S., et al. “What intensivists need to know about cytomegalovirus infection in immunocompromised ICU patients”. Intensive Care Medicine1 (2025): 39-61.
5. Bateman CM., et al. “Cytomegalovirus infections in children with primary and secondary immune deficiencies”. Viruses10 (2021): 2001.
6. Bate SL., et al. “Cytomegalovirus seroprevalence in the United States: the National Health and Nutrition Examination Surveys, 1988-2004”. Clinical Infectious Diseases11 (2010): 1439-1447.
7. Kotton CN., et al. “The third international consensus guidelines on the management of cytomegalovirus in solid-organ transplantation”. Transplantation6 (2018): 900-931.