Prolonged febrile illness with systemic inflammation
in elderly patients often presents a diagnostic challenge. Common bacterial or
viral pathogens are frequently considered, but intracellular zoonotic
infections such as rickettsioses are easily overlooked, especially when
classical signs such as rash or eschar are absent. Rickettsial infections may
also trigger a hyperinflammatory response resembling hemophagocytic
lymphohistiocytosis (HLH), adding further complexity. We describe a case of
probable Typhus group rickettsiosis in an elderly male, initially treated as
culture-negative sepsis, who showed a dramatic response to doxycycline therapy.
Case
Presentation
Mr. Maxwell James Roberts, a 76-year-old man,
presented in early June 2025 with a one-week history of intermittent colicky
abdominal pain, fevers, malaise, and diaphoresis. His background included type
2 diabetes mellitus, ischaemic heart disease, hyperlipidaemia, gout, and
anxiety exacerbated by recent bereavement. He had undergone a routine
colonoscopy with polypectomy approximately four weeks prior.
On presentation to the Emergency Care Centre (ECC), he
was hemodynamically stable but febrile. Initial investigations showed a CRP of
21 mg/L, with no focal findings on clinical examination. A CT scan of the
abdomen and pelvis demonstrated bibasal lung atelectasis, fatty liver,
diverticulosis, and a stable 13 mm adrenal nodule, with no evidence of
diverticulitis or abscess formation. Empirical intravenous ceftriaxone and
metronidazole were commenced. Despite therapy, his fevers persisted and
inflammatory markers rose substantially over the following days. On 9 June
2025, blood cultures grew Staphylococcus hominis in both aerobic bottles. Repeat
cultures were sterile. CRP increased to 158 mg/L, and he developed acute kidney
injury with creatinine rising from 126 to 147 µmol/L. Hypoalbuminemia (23 g/L),
transaminitis (ALT 217 U/L, AST 154 U/L, GGT 239 U/L), and elevated ALP (181
U/L) were also noted. Ferritin was markedly elevated at 1770 µg/L, and
procalcitonin was 9.47 µg/L. The white cell count remained within normal
limits, but there was persistent lymphopenia (0.30 ×10?/L) and borderline
thrombocytopenia (117 ×10?/L).
Respiratory virus PCR testing—including SARS-CoV-2,
Influenza A/B, RSV, parainfluenza, adenovirus, and rhinovirus—was negative.
Serological testing for hepatitis A, B, and C was negative. Epstein-Barr virus
(EBV) and cytomegalovirus (CMV) serology confirmed past exposure (IgG positive,
IgM negative). Urine and sputum cultures were negative. Q fever serology and
PCR were negative. Rickettsial
serology, however, revealed a Typhus Group IgG titre of 1:512, consistent with
either recent or past infection. Spotted fever and scrub typhus antibodies were
not detected. In consultation with the Infectious Diseases team, oral
doxycycline 100 mg twice daily was commenced on 19 June 2025. Following initiation of doxycycline, the
patient became afebrile within 48 hours. His appetite and functional status
improved, and inflammatory markers declined dramatically, with CRP falling to 7
mg/L. Renal and hepatic parameters also improved, and lymphocyte and platelet
counts began to recover. A
transthoracic echocardiogram was performed on 12 June 2025 to evaluate for
endocarditis in the setting of Staphylococcus hominis bacteremia. The study
demonstrated normal left and right ventricular size and function, with a
preserved ejection fraction of 63% and only grade 1 diastolic dysfunction.
There was no significant valvular disease or vegetation identified on any
valve, and no pericardial effusion. The inferior vena cava was normal in size
with appropriate respiratory variation.