Diabetes and Infections

The relationship between diabetes and infections is bidirectional, complex, and clinically important in every aspect of diabetes care. Chronic hyperglycemia impairs innate and adaptive immunity in multiple simultaneous ways — reducing neutrophil chemotaxis, phagocytic killing, and the oxidative burst, while also impairing T-cell activation and macrophage function. These immune defects mean that adults with poorly controlled diabetes and infections interact in a reinforcing cycle: hyperglycemia worsens immune function, which allows infections to become more severe; infections then trigger cortisol and catecholamine release that dramatically elevates blood glucose (infection-induced hyperglycemia), which further impairs immune defenses. Adults with diabetes are not just slightly more susceptible to infections — they tend to get certain infections far more frequently than people without diabetes, experience more severe presentations, have higher rates of complications and hospitalization, face higher antibiotic failure rates (because hyperglycemia impairs antibiotic efficacy), and carry higher mortality from serious infections including pneumonia, influenza, urinary tract infection, and skin and soft tissue infections. Understanding which infections are most concerning in diabetes, why they are harder to treat, and what preventive strategies — particularly vaccination — can reduce risk is an essential part of comprehensive diabetes self-management.

Why Diabetes Increases Infection Risk: The Immunological Mechanisms

Multiple simultaneous immunological defects drive the elevated susceptibility to diabetes and infections — and understanding them explains why infection prevention (particularly vaccination) and rapid treatment are so critical:

• Neutrophil dysfunction — the front line of bacterial defense is impaired: Neutrophils are the white blood cells that respond first to bacterial infection — chemotaxing (migrating toward the site of infection), phagocytosing (engulfing) bacteria, and killing them through oxidative burst (release of reactive oxygen species including hydrogen peroxide and hypochlorous acid). In hyperglycemia, all three of these functions are impaired: neutrophils move more slowly toward infection sites (impaired chemotaxis), engulf bacteria less efficiently (reduced phagocytosis), and produce a weaker oxidative burst (reduced intracellular killing capacity). The degree of neutrophil dysfunction correlates directly with blood glucose levels — acute hyperglycemia above 200 mg/dL produces measurable impairment of neutrophil killing within hours, and chronic hyperglycemia produces sustained structural changes in neutrophils. This is why poorly controlled diabetes is a consistent predictor of surgical site infections, wound infections, and bacteremia after procedures. The A1C monitoring that tracks chronic glucose control is in our A1C testing schedule guide.
• T-cell and macrophage dysfunction — adaptive immunity is compromised: Beyond innate immunity, chronic hyperglycemia also impairs the adaptive immune response — T-cell proliferation in response to antigenic stimulation is reduced, T-cell cytotoxicity is impaired, and macrophage antigen presentation is less effective. This makes adults with diabetes less effective at generating immune memory responses and less capable of controlling intracellular pathogens (including Mycobacterium tuberculosis — which is three to eight times more common in adults with diabetes globally — and certain fungal infections including Cryptococcus and Histoplasma). The impaired vaccine response observed in some adults with poorly controlled diabetes (reduced antibody titers after influenza and hepatitis B vaccination compared with adults with well-controlled diabetes or without diabetes) reflects this adaptive immune impairment — a further motivation for maintaining good glucose control.
• Structural defects — neuropathy, vascular disease, and microbiome changes: Beyond immune function, diabetes creates structural defects that increase infection susceptibility. Peripheral neuropathy impairs the detection of skin injuries that become portals for bacterial entry. Peripheral arterial disease reduces blood supply to tissues — limiting delivery of white blood cells and antibiotics to infection sites. Gastroparesis (delayed gastric emptying from autonomic neuropathy) creates bacterial overgrowth in the upper gastrointestinal tract and impairs absorption of oral antibiotics. Chronic hyperglycemia changes the composition of the urinary microbiome and increases urinary glucose (glucosuria), creating a high-sugar environment that promotes bacterial growth in the bladder. The neuropathy context that explains structural infection susceptibility is in our diabetic neuropathy: symptoms and prevention guide. The broader diabetes complications context is in our diabetes complications: what adults should know guide.

The Most Important Infections in Adults With Diabetes

While adults with diabetes and infections face increased susceptibility across many infection types, several specific infections are particularly important to recognize and prevent:

• Urinary tract infections — frequency, severity, and complications unique to diabetes: UTIs occur two to four times more frequently in women with diabetes than in women without diabetes. In adults with diabetes, UTIs carry a higher risk of complications that are rare in the general population: emphysematous cystitis (gas-forming UTI in the bladder wall, caused by fermentation of urinary glucose by bacteria), emphysematous pyelonephritis (gas-forming kidney infection — a life-threatening emergency requiring immediate drainage and sometimes nephrectomy), and papillary necrosis (death of the renal papillae from ischemia combined with infection, presenting with flank pain and hematuria). Adults with diabetes and symptoms of UTI (dysuria, frequency, urgency, pelvic pain, or flank pain) should seek prompt evaluation rather than treating empirically without culture — because the organisms causing complicated UTIs in diabetes (including Klebsiella, Enterococcus, and ESBL-producing Enterobacterales) often require different antibiotics than the E. coli that causes most uncomplicated UTIs in healthy adults. The kidney function monitoring that detects complications from recurrent UTIs is in our eGFR and kidney function in diabetes guide.
• Skin and soft tissue infections — cellulitis, necrotizing fasciitis, and fungal skin infections: Adults with diabetes have significantly higher rates of skin and soft tissue infections — including cellulitis (superficial skin infection), erysipelas, and the far more dangerous necrotizing fasciitis (rapidly spreading deep soft tissue infection that destroys fascia and requires immediate surgical debridement). The factors driving this elevated risk include: skin dryness and cracking from dehydration (glycosuria produces osmotic diuresis), impaired neutrophil function at the skin level, reduced blood supply impairing immune response delivery, and neuropathy-related foot injuries that provide bacterial portals. Fungal skin infections (tinea pedis — athlete’s foot; tinea corporis — ringworm; intertriginous Candida in skin folds) are also substantially more common in adults with poorly controlled diabetes — glucose in skin secretions promotes fungal growth. Recurrent or refractory skin infections should prompt glucose evaluation in adults not already diagnosed with diabetes. The wound healing guide that covers the management of skin injuries in diabetes is our diabetes and wound healing article.
• Respiratory infections — pneumonia and influenza carry higher mortality in diabetes: Adults with diabetes are three to five times more likely to die from influenza and pneumonia than adults without diabetes. This dramatically elevated mortality reflects impaired neutrophil and macrophage function in the lung, impaired mucociliary clearance, and the physiological consequences of infection-induced hyperglycemia (stress hyperglycemia from cortisol and catecholamine release further impairs immune function during the acute infection). Pneumococcal pneumonia (caused by Streptococcus pneumoniae) is particularly severe in adults with diabetes and is preventable by vaccination. Influenza-associated mortality in adults with diabetes is substantially reduced by annual influenza vaccination. The ADA recommends annual influenza vaccination, one-time PCV15 or PCV20 pneumococcal vaccination, COVID-19 vaccination with updated booster doses, hepatitis B vaccination, and RSV vaccination for eligible adults — all specifically because of the dramatically elevated mortality from these preventable infections in adults with diabetes. The complete annual monitoring and vaccination checklist is in our annual diabetes care checklist. The CDC’s pneumococcal vaccination guidance, the ADA’s illness management resources, and the NIDDK’s diabetes complication prevention guide provide authoritative clinical information on infection prevention and management in adults with diabetes.

Preventing Infections in Diabetes: Vaccination and Daily Practices

Preventing diabetes and infections requires a dual approach: reducing infection exposure and optimizing immune function through blood glucose control, combined with vaccination against the most dangerous preventable infections:

• Vaccination — the most impactful infection prevention strategy available to adults with diabetes: The ADA and CDC both recommend a specific vaccination schedule for adults with diabetes that differs from the standard adult vaccination schedule in several important ways. Annual influenza vaccination is recommended for all adults with diabetes regardless of age — because the mortality difference from influenza between adults with and without diabetes is greatest precisely in the 18–64 age group (where adults without diabetes typically have low influenza mortality, making the relative mortality elevation in adults with diabetes especially dramatic). Pneumococcal vaccination — using PCV20 (or PCV15 followed by PPSV23 8–12 weeks later) — is recommended for all adults with diabetes who have not previously been vaccinated. Hepatitis B vaccination (three-dose series for adults under 60 who have not previously been vaccinated, two-dose series for adults 60 and older who elect vaccination) is recommended because adults with diabetes have higher rates of hepatitis B transmission through shared glucose monitoring equipment and higher rates of chronic hepatitis B infection. COVID-19 vaccination with updated boosters should be kept current. RSV vaccination with a single dose is recommended for adults 60 and older with diabetes as a high-risk condition. HPV vaccination for adults under 26, and catch-up shingles (recombinant zoster) vaccination for adults 50 and older, complete the standard vaccination recommendations for adults with diabetes. The annual care checklist that coordinates vaccination with all other diabetes monitoring is in our annual diabetes care checklist.
• Blood glucose optimization — improving immune function at its root cause: Every 1% reduction in A1C in an adult with poorly controlled Type 2 diabetes produces measurable improvement in neutrophil function, wound healing rates, and infection outcomes. Prioritizing blood glucose control through medication adherence, dietary management, and physical activity is not only about preventing microvascular complications (neuropathy, retinopathy, nephropathy) — it is also about maintaining the immunological capacity to fight infections effectively. During any active infection, blood glucose typically rises significantly from stress hormones — adults with diabetes should monitor blood glucose more frequently during illness, maintain hydration, and follow their healthcare provider’s sick day guidelines (which may include insulin dose adjustments and ketone testing for adults with Type 1 diabetes or insulin-dependent Type 2 diabetes). The A1C testing guide is our A1C testing schedule guide.
• Skin and wound care — preventing bacterial entry portals: Many serious infections in adults with diabetes begin with minor skin injuries that go unnoticed because of neuropathy. Daily foot inspection (described in detail in our diabetic foot problems: prevention and care guide), keeping skin moisturized to prevent cracking, prompt cleaning and covering of any skin break, and avoiding practices that increase infection risk (self-treatment of calluses with keratolytic agents, walking barefoot in public facilities where fungal exposure is high) all reduce infection entry. Any skin wound that shows signs of infection — redness, warmth, swelling, purulent discharge, red streaking (lymphangitis), or fever — requires prompt medical evaluation in an adult with diabetes. The wound healing guide that covers comprehensive wound management is our diabetes and wound healing article.
• SGLT2 inhibitor-associated genital yeast infections — a medication-specific consideration: SGLT2 inhibitors (empagliflozin, canagliflozin, dapagliflozin) — increasingly prescribed for their cardiovascular and kidney-protective benefits in adults with Type 2 diabetes — cause increased glucosuria (glucose in the urine) as their mechanism of glucose lowering. This elevated urinary glucose promotes Candida (yeast) growth in the genital area, causing mycotic genital infections (vulvovaginal candidiasis in women, balanitis in men) at rates approximately five times higher than in adults not on SGLT2 inhibitors. These infections respond to standard antifungal treatment and are manageable, but adults starting SGLT2 inhibitors should be counseled to expect this risk and seek early treatment if symptoms develop rather than attributing genital discomfort to another cause. Good genital hygiene and prompt treatment of early candidiasis reduce the risk of recurrence. The comprehensive diabetes complications framework is in our diabetes complications: what adults should know guide. The CDC pneumococcal vaccination guidance, the ADA’s illness management in diabetes, and the NIDDK’s diabetes prevention guide provide authoritative clinical information on infection prevention in adults with diabetes.

Sick Day Management in Diabetes: What to Do When Infections Strike

When an infection occurs in an adult with diabetes and infections, specific management principles apply that differ from infection management in adults without diabetes — because infection-induced hyperglycemia can escalate to diabetic ketoacidosis (DKA) in Type 1 diabetes and insulin-dependent Type 2 diabetes, and because hyperglycemia during infection worsens outcomes of the infection itself:

• Blood glucose monitoring every 2–4 hours during any significant infection: Any significant illness — fever, vomiting, diarrhea, a serious skin infection, or pneumonia — should trigger more frequent blood glucose monitoring. Stress hormones released during infection (cortisol, glucagon, epinephrine) drive significant blood glucose elevation in adults with diabetes, even if the person is eating less than usual. Adults with Type 1 diabetes and adults with Type 2 diabetes requiring insulin should monitor blood glucose every 2–4 hours during illness, and adults with well-controlled Type 2 diabetes on non-insulin agents should increase monitoring frequency to identify unexpected hyperglycemia. The goal is to identify blood glucose above 240–300 mg/dL that may require insulin supplementation even in adults who do not normally use insulin, and to identify patterns that indicate worsening glycemic control requiring urgent clinical contact.
• Ketone testing for adults with Type 1 diabetes and insulin-dependent Type 2 diabetes: Adults with Type 1 diabetes (and some with insulin-dependent Type 2 diabetes) should test urine or blood ketones during illness whenever blood glucose exceeds 250 mg/dL, when nausea or vomiting is present, or when symptoms of DKA are developing (nausea, vomiting, abdominal pain, deep rapid breathing, fruity breath odor, confusion). Blood ketone testing (using a meter that measures beta-hydroxybutyrate) is more sensitive than urine ketone testing and provides faster feedback. Moderate or large urine ketones (2+ or higher) or blood ketones above 1.5 mmol/L in the setting of hyperglycemia during illness require immediate contact with a healthcare provider or emergency department evaluation — because DKA is a life-threatening emergency that requires intravenous insulin and fluid replacement. The diabetes emergency guide that covers DKA recognition and emergency response is our when diabetes symptoms become an emergency article.
• Hydration — maintaining fluid intake during infection to prevent dehydration and hyperglycemic crises: Vomiting and diarrhea from gastrointestinal infections, fever from respiratory infections, and reduced oral intake from illness all promote dehydration in adults with diabetes. Dehydration worsens hyperglycemia (by increasing plasma glucose concentration) and increases the risk of hyperosmolar hyperglycemic state (HHS) in adults with Type 2 diabetes — a serious complication characterized by very high blood glucose (often above 600 mg/dL), severe dehydration, and altered mental status without significant ketosis. Adults with diabetes who cannot maintain oral fluid intake during illness (due to persistent vomiting) should seek emergency evaluation for intravenous fluid replacement rather than attempting to manage at home. Small sips of clear fluids (water, broth, diluted juice) every 15–30 minutes may be tolerated even when larger volumes trigger vomiting — but any adult with diabetes who is significantly dehydrated, confused, or unable to maintain any oral intake should not delay seeking emergency care.
• Medication management during infection — which drugs to hold and which to continue: Certain diabetes medications may need to be held or adjusted during significant illness. Metformin should be held during acute illness with significant dehydration, vomiting, or any condition that reduces renal blood flow (including severe infection with hypotension), because dehydration-induced renal impairment increases metformin accumulation and lactic acidosis risk. SGLT2 inhibitors should be held during prolonged fasting, significant illness, or any surgical procedure — because euglycemic DKA (DKA with relatively normal blood glucose) is a rare but serious complication of SGLT2 inhibitors in physiological stress states. Adults who take insulin should continue insulin during illness (insulin requirement does not disappear just because appetite is reduced — stress hormones will drive hyperglycemia regardless of food intake) and may need supplemental correction doses based on blood glucose monitoring. Contact with a diabetes care provider or use of a provided sick day protocol is recommended for any significant illness that lasts more than 24 hours or causes more than two episodes of vomiting or diarrhea. The annual monitoring and care coordination is in our annual diabetes care checklist. The CDC’s vaccination guidance for adults, the ADA’s sick day management resources, and the NIDDK’s diabetes complication prevention provide authoritative clinical information on managing infections and illness in adults with diabetes.

Adults with diabetes and recurrent infections — particularly recurrent UTIs, recurrent skin infections, or recurrent fungal infections — should have their A1C reviewed and their blood glucose management optimized, because recurrent infections in adults with diabetes are frequently a marker of suboptimal glucose control rather than simply bad luck. The A1C testing guide that tracks the glucose control underlying infection susceptibility is our A1C testing schedule guide. The diabetic kidney disease guide that covers complications from recurrent UTIs is our diabetic kidney disease: early warning signs article. The urine albumin guide that monitors kidney involvement in recurrent infections is our urine albumin test and diabetes article.

Sources: ADA — Standards of Medical Care in Diabetes, vaccination recommendations and infection risk in diabetes; CDC — vaccination guidelines for adults with diabetes; NIDDK — infection prevention in diabetes; ADA — illness management and sick day rules; UTI complication rates in diabetes — emphysematous cystitis, emphysematous pyelonephritis, papillary necrosis; neutrophil dysfunction in hyperglycemia — impaired chemotaxis, phagocytosis, and oxidative burst; T-cell dysfunction in chronic hyperglycemia — reduced proliferation and cytotoxicity; tuberculosis risk in adults with diabetes (three to eight times elevated globally); influenza and pneumonia mortality in adults with diabetes (three to five times general population mortality); Staphylococcus aureus bacteremia case fatality rate in diabetes vs controls; COVID-19 severity and mortality in adults with diabetes and elevated A1C; Candida infection prevalence in poorly controlled diabetes; SGLT2 inhibitor-associated urogenital yeast infections; glucosuria-promoted bacterial growth in the urinary tract; annual influenza vaccination effectiveness in adults with diabetes; pneumococcal vaccination recommendations — PCV15, PCV20, PPSV23 schedules for adults with diabetes; hepatitis B vaccination in adults with diabetes (three-dose series for adults under 60); sick day management — insulin dose adjustment, ketone monitoring, when to seek emergency care.