Atypical Presentations of Infections in the Elderly

Atypical presentation means an infection that presents without its classical localising or systemic features, and instead declares itself through non-specific geriatric syndromes.

It matters because atypical presentation delays diagnosis and treatment, and is independently associated with higher mortality. Underreporting of symptoms, impaired communication, coexisting disease and altered physiological responses all contribute.

Immunosenescence: thymic involution reduces T-cell production and function; cell-mediated immunity falls markedly, humoral immunity to a lesser degree; B-cell numbers and phagocytic and complement function are relatively preserved. Adaptive immunity is affected far more than innate immunity.

Inflammageing: chronic low-grade inflammation with raised IL-6 and TNF raises the baseline CRP and blunts the incremental acute-phase response, so a "modest" CRP rise may represent severe illness.

Impaired thermoregulation: reduced pyrogenic cytokine production, lower muscle mass, blunted vasoconstriction and a lower baseline temperature together produce the blunted febrile response.

Loss of barrier and reserve: impaired cough reflex, reduced mucociliary clearance and decreased mucus secretion predispose to aspiration; prostatic obstruction predisposes men to urinary infection; skin thinning and pressure sores create portals of entry.

Comorbidity masking: existing chronic disease conceals acute infection. Septic arthritis characteristically occurs in an already abnormal joint, so synovial fluid must be aspirated whenever an older patient has an "acute exacerbation" of joint disease.

Delirium or acute confusion — the single commonest atypical presentation. Infections not involving the CNS routinely cause confusion in the elderly, particularly with pre-existing dementia.

Falls and unexplained loss of mobility — a fall in a previously ambulant older person should prompt a search for infection.

Acute functional decline — sudden inability to perform activities of daily living. "Acute unexplained functional deterioration should alert the physician to a potential acute infectious process."

New or worsening incontinence, anorexia and reduced oral intake, generalised weakness and fatigue, and failure to cooperate with carers.

Absence of fever in one-third of cases, and frank hypothermia, which predicts mortality. Absence of leucocytosis does not exclude bacterial infection.

Decompensation of a chronic condition — new atrial fibrillation, worsening heart failure, or hyperglycaemic crisis may be the only presentation of sepsis.

Pneumonia: fever and cough are absent in 30–40% of elderly cases. Look instead for tachypnoea above 30/min, tachycardia above 110/min, confusion or falls. Pneumonia remains the commonest infective cause of death in geriatric patients.

Urinary tract infection: presents as altered mental status rather than dysuria; over a quarter of over-70s with bacteraemic UTI present with confusion. Do not send urine culture in an asymptomatic resident — asymptomatic bacteriuria is common and should not be treated in the absence of obstructive uropathy.

Intra-abdominal sepsis: appendicitis and diverticulitis present without guarding or rigidity; failure to seek medical attention contributes to the higher morbidity and mortality of appendicitis in older adults.

Tuberculosis: presents as weight loss, anorexia and failure to thrive rather than haemoptysis; reactivation is favoured by malnutrition and comorbidity. A useful rule — suspect tuberculosis when an older patient is inexplicably failing. Rates are higher in long-term care than in the community.

COVID-19 and respiratory viruses: Pathy's records that delirium and falls are common atypical presentations of COVID-19 in older people, with delirium in around 30% of hospitalised cases and up to 70% in severe disease. Atypical presentation should trigger testing, not reassure.

"In the elderly, the geriatric syndromes are the symptoms of infection — delirium, falls, functional decline, incontinence and anorexia."

"Fever is absent in 30–50% of older patients with serious infection, and hypothermia carries a worse prognosis than fever."

"Absence of leucocytosis does not exclude bacterial infection."

"Any acute unexplained functional deterioration is an infection until proven otherwise."

"Standard sepsis screening tools are less sensitive in older adults, so I would rely on change from the patient's own baseline together with lactate and procalcitonin."

Close with the classical Osler quotation in your own words: in old age pneumonia may be latent, with slight cough, ill-defined signs, and constitutional symptoms out of all proportion.