Salmonella Typhimurium pneumonia in a patient with multiple myeloma

Introduction

Non-typhoidal salmonella are common pathogens of the gastrointestinal tract. The burden of invasive non-typhoidal salmonella (NTS) disease has frequently been underestimated in endemic regions. ¹ Invasive bacteraemia due to NTS is seen in immunosuppressed individuals, steroid users, patients with chronic liver and kidney infections, and extremes of age. ¹ Studies from tropical Africa have frequently described NTS as the most common cause of paediatric bacteraemia. ² Lung involvement due to these organisms in the form of lung abscesses, empyema and bronchopneumonia do occur but are relatively rare. ³ We describe a case of pneumonia due to Salmonella Typhimurium in a patient with multiple myeloma.

Case report

A 60-year-old man presented with complaints of back pain, nausea and loss of appetite for the preceding 5 days. A diagnosis of multiple myeloma had been made 2 years before, and a posterior fusion of T4 had been performed 2 years previously. He was undergoing haemodialysis for chronic renal failure for the last 6 months. On examination the patient was conscious, oriented with no pallor or oedema. He was tachypnoeic, had a pulse rate of 110/minute and a blood pressure of 110/70 mmHg.

Laboratory investigations showed a leucocyte count of 9,230/mm³ and a haemoglobin level of 11.3 mg/dl. Serum electrolytes showed a sodium level of 141 mmol/L, potassium of 6.3 mmol/L, calcium of 9.2 mmol/L, creatinine of 808.86 mmol/L, uric acid of 493.68 umol/L and blood urea of 158.8 mmol/L. As the evaluation showed severe renal failure, metabolic acidosis and hyperkalaemia, haemodialysis was re-initiated via a right femoral catheter. On the second day of admission, he was transferred to intensive care because of extreme restlessness, acute onset dyspnoea, oxygen desaturation, tachycardia and hypotension. The pulse rate was 160/minute; blood pressure 68/36 mmHg; respiratory rate 38/minute and SpO2 73%. There were bilateral rhonchi and coarse crepitations audible in the infra-axillary area. His conscious level dropped to a GCS of 9/15. The chest radiograph showed bilateral lower lobe infiltrates. The patient was intubated and ventilated mechanically. A blood culture and endotracheal tube aspirate were sent for culture and the patient was commenced on piperacillin tazobactam 4.5 gm 6-hourly. Over the next 24 h he deteriorated, developing septic shock, and died.

Non-lactose fermenting Gram-negative bacilli were cultured from the blood as well as from the endotracheal tube aspirate. The organism was identified as Salmonella spp by Vitek2 compact (98% probability), and showed agglutination with Salmonella O antisera Group B (factor 4) as well as Salmonella H antisera i (CRI, Kasauli); hence it was identified as Salmonella Typhimurium. It was sensitive to ampicillin, cotrimoxazole, nalidixic acid, ciprofloxacin, chloramphenicol and ceftriaxone.

Discusssion

Non-typhoidal salmonella are frequently implicated in gastroenteritis, bacteraemia, focal infections such as osteomyelitis, septic arthritis, endocarditis and meningitis. ⁴ Pleuropulmonary infections due to salmonella have been reported but pneumonia is rare. ⁵

Individuals with impaired cell-mediated immunity from HIV, corticosteroid therapy, diabetes mellitus, chemotherapy and malignancy are predisposed to salmonellosis. The patient described in this case was one such. Although Salmonella pneumonia is rare, prior lung abnormalities predispose to lung involvement with non-typhoidal Salmonellae. ⁶ In the present case the isolation of the organism from the blood and endotracheal secretions, the presence of pulmonary patches on chest radiography, and the history of malignancy treated with radiotherapy and chemotherapy makes the diagnosis a strong possibility. Alternatively, profound septicemia with Salmonella spp in immunosuppressed and chronically ill individuals can lead to isolation of the organism from various sites. Co-morbidities such as pulmonary oedema and ARDS can be attributed to cause respiratory symptoms. However, in this case bilateral lower zone peripheral nodules in the lung make pneumonia a more likely possibility than ARDS and pulmonary oedema which show perihilar and pericardiac region congestion.

A majority of patients with Salmonella pneumonia have positive blood cultures which may indicate a hematogenous spread. ⁷ However, stool culture was not performed in this case, owing to the lack of gastrointestinal symptoms.

Treatment of Salmonella pneumonia requires oral or parenteral antibiotics for 2 weeks. Mortality is high in immunosuppressed patients with Salmonella pneumonia with some studies reporting it to be as high as 63%. ⁸ The underlying morbidity of these patients also contributes to the high mortality.

Although pleuropulmonary infections due to non-typhoidal salmonellae are rare, they should be suspected in patients with malignancy and immunosuppressive therapy. Second, empirical therapy should cover these pathogens in this group of patients owing to the high mortality associated with Salmonella pneumonia. Finally, general measures in the management of critically ill patients such as provision of appropriate levels of care, early institution of treatment for sepsis when identified and strict adherence to sepsis bundles are practices which should always be prioritised.