Types of Infections
- Bacterial infections caused by pathogens such as Mycobacterium tuberculosis, Staphylococcus aureus, Escherichia coli, Clostridium botulinum, and Salmonella spp.
- Viral infections caused by pathogens such as HIV, Rhinovirus, Lyssaviruses (e.g., Rabies virus, Ebolavirus), and Severe acute respiratory syndrome coronavirus 2
- Fungal infections including yeasts like Candida, filamentous fungi like Aspergillus, Pneumocystis species, and dermatophytes
- Parasitic infections caused by unicellular organisms like malaria and Toxoplasma, and macroparasites like nematodes, tapeworms, and flukes
- Infections caused by arthropods such as ticks, mites, fleas, and lice, often referred to as infestations
- Prion infections, although they do not secrete toxins

Signs and Symptoms of Infections
- General symptoms of infection include fatigue, loss of appetite, weight loss, fevers, night sweats, chills, aches, and pains
- Specific symptoms can affect individual body parts, such as skin rashes, coughing, or a runny nose
- Some infectious diseases may be asymptomatic or cause no illness in a host
- Infections can be localised or systemic, with viral infections often involving multiple body parts and bacterial infections causing localised redness, heat, swelling, and pain
- Pus and milky-colored liquid are signs of infection in wounds

Bacterial vs. Viral Infections
- It can be difficult to distinguish between bacterial and viral infections based on symptoms alone
- Viral infections are often systemic, involving multiple body parts, while bacterial infections are characterised by localised pain and symptoms
- Antibiotics can cure bacterial infections, but they are ineffective against viral infections
- Viral infections can cause itching or burning sensations, while bacterial infections may produce pus and localised pain
- Pain on one side of the throat or in one ear is more indicative of a bacterial infection

Pathophysiology of Infections
- Infections follow a chain of events called the chain of infection or transmission chain
- The chain includes the infectious agent, reservoir, entry into a susceptible host, exit, and transmission to new hosts
- Each step must occur in order for an infection to develop
- Health care workers target the chain of infection to prevent and treat infections
- Colonization is the initial stage of infection, where organisms successfully enter the body, grow, and multiply

Diagnosis of Infectious Diseases
- Medical history and physical examination
- Culture of infectious agents
- Microscopic examination and detection of pathogen-produced substances
- Tests for antigens or antibodies in body fluids
- Imaging techniques (X-rays, CAT scans, etc.) for internal abnormalities
- Presenting symptoms aid in diagnosis
- Pathognomonic signs are rare but indicative of a specific disease
- Not all infections are symptomatic
- Certain symptoms in children increase the risk of serious infection
- Additional diagnostic techniques are often required to confirm suspicions
- Microbiological culture is used to isolate a pathogen from a clinical specimen
- Microscopy is an important tool in the diagnosis of infectious diseases
- Biochemical tests detect metabolic or enzymatic products characteristic of infectious agents
- Animal culture and xenodiagnosis can be used for identification of certain pathogens
- PCR-based diagnostics are becoming the gold standard for diagnosing infectious agents
- Metagenomic sequencing is a promising diagnostic test for identifying the cause of infection
- Diagnostic tests are indicated when they can aid in treatment or prevention of a disease
- Symptomatic infections, inapparent infections, latent infections, acute infections, chronic infections, and subacute infections are different classifications of infections.