question: Why are viral infections more common than bacterial infections?
comment: Bacteria can grow on their own, so they can form colonies in the blood as themselves, not as infections within human cells. Viruses, on the other hand, have to hijack human cells in order to create more viruses. This means that your immune system can immediately recognize a bacterial infection, but it can take some time for the immune system to recognize viruses because they look a lot like normal human cells. This delayed response is why we see more viral diseases than nonviral ones, because often our bodies kill bacteria before they can make us sick. If a virus takes time to be detected, that gives the virus a better chance of making us sick. Also, in wealthy countries we have a lot of antibiotics all around us. (We could argue that we have TOO many, leading to more superbugs, but that's beside the point.) The number of antibiotics and disinfectants we have helps to kill bacteria; viruses are harder to kill, generally speaking, so that also increases the number of viral infections compared to bacterial ones.
passages: There is evidence of an association between BV and increased rates of sexually transmitted infections such as HIV/AIDS. BV is associated with up to a six-fold increase in HIV shedding. BV is a risk factor for viral shedding and herpes simplex virus type 2 infection. BV may increase the risk of infection with or reactivation of human papillomavirus (HPV).
  
  In addition, bacterial vaginosis as an intercurrent disease in pregnancy may increase the risk of pregnancy complications, most notably premature birth or miscarriage.
   Bacterial and viral infections can both cause the same kinds of symptoms. It can be difficult to distinguish which is the cause of a specific infection. It's important to distinguish, because viral infections cannot be cured by antibiotics.
  
  Section::::Pathophysiology.
   The cell from which the virus itself buds will often die or be weakened and shed more viral particles for an extended period. The lipid bilayer envelope of these viruses is relatively sensitive to desiccation, heat, and detergents, therefore these viruses are easier to sterilize than non-enveloped viruses, have limited survival outside host environments, and typically must transfer directly from host to host. Enveloped viruses possess great adaptability and can change in a short time in order to evade the immune system. Enveloped viruses can cause persistent infections.
  
  Section::::Enveloped examples.
  
  Classes of enveloped viruses that contain human pathogens:
   NTM diseases have been seen in most industrialized countries, where incidence rates vary from 1.0 to 1.8 cases per 100,000 persons. Recent studies, including one done in Ontario, Canada, suggest that incidence is much higher. Pulmonary NTM is estimated by some experts in the field to be at least ten times more common than TB in the U.S., with at least 150,000 cases per year.
   Traditional viral culture has been generally superseded by shell vial culture, in which the sample is centrifuged onto a single layer of cells and viral growth is measured by antigen detection methods. This greatly reduces the time to detection for slow growing viruses such as cytomegalovirus, for which the method was developed. In addition, the centrifugation step in shell viral culture enhances the sensitivity of this method because after centrifugation, the viral particles of the sample are in close proximity to the cells.
  
  Human and monkey cells are used in both traditional viral culture and shell vial culture.
   One of the bacterial diseases with the highest disease burden is tuberculosis, caused by "Mycobacterium tuberculosis" bacteria, which kills about 2 million people a year, mostly in sub-Saharan Africa. Pathogenic bacteria contribute to other globally important diseases, such as pneumonia, which can be caused by bacteria such as "Streptococcus" and "Pseudomonas", and foodborne illnesses, which can be caused by bacteria such as "Shigella", "Campylobacter", and "Salmonella". Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis, and leprosy. Pathogenic bacteria are also the cause of high infant mortality rates in developing countries.
   Viruses tend to outnumber bacterial abundance by about ten times and phytoplankton by about a hundred times in the upper mixing layer and bacterial abundance tends to decrease with depth, while phytoplankton remain closer to shallow depths. The effects of the viral shunt are more pronounced in the upper mixing layer. Viruses found can be non-specific (broad host range), abundant, and can infect all forms of microbes. Viruses are a magnitude higher in abundance in almost all aquatic locations compared to their microbial hosts, allowing high rates/levels of microbial infection.
   BV is the most common infection of the vagina in women of reproductive age. The percentage of women affected at any given time varies between 5% and 70%. BV is most common in parts of Africa, and least common in Asia and Europe. In the United States, about 30% of those between the ages of 14 and 49 are affected. Rates vary considerably between ethnic groups within a country.
   Biological air pollution also can lead to the infections. Small, invading organisms in human body, such as bacteria, viruses, fungi, or parasites, can cause infections in the pulmonary system. There are variety of infections because many different organisms can cause the infections.
   The respiratory system is very prone to developing infections in the lungs. Infants and older adults are more likely to develop infections in their lungs, because their lungs are not as strong in fighting off these infections. Most of these infections used to be fatal, but with new research and medicine, they are now treatable. With bacterial infections, antibiotics are prescribed, while viral infections are harder to treat, but still curable.
  
  The common cold/flu is the most common cause for the upper respiratory tract infection, which can cause more serious illness that can develop in the lower respiratory 
   where formula_2 is the multiplicity of infection or MOI, formula_1 is the number of infectious agents that enter the infection target, and formula_6 is the probability that an infection target (a cell) will get infected by formula_1 infectious agents.
  
  In fact the infectivity of the virus or bacteria in question will alter this relationship. One way around this is to use a functional definition of infectious particles rather than a strict count, such as a plaque forming unit for viruses.
   Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then they touch their eyes or nose. Other viral infections occur when contaminated airborne droplets are inhaled through the mouth or nose. Once in the upper airway, the viruses may make their way in the lungs, where they invade the cells lining the airways, alveoli, or lung parenchyma. Some viruses such as measles and herpes simplex may reach the lungs via the blood. The invasion of the lungs may lead to varying degrees of cell death. When the immune system responds to the infection, even more lung damage may occur. Primarily white blood cells, mainly mononuclear cells, generate the inflammation. As well as damaging the lungs, many viruses simultaneously affect other organs and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.
   First, there is an extreme bottleneck in viral diversity at the time of sexual transmission. Second, transmission tends to occur early in infection before immune selection has had a chance to operate. Finally, the replicative fitness of a viral strain (measured in transmissions per host) is largely extrinsic to virological factors, depending more heavily on behaviors in the host population. These include heterogeneous sexual and drug-use behaviors.
   Viruses infecting bacteria, called bacteriophages, are a common and diverse group of viruses and are thought to be the most abundant form of biological entity in aquatic environments, because their hosts, bacteria, are typically the numerically dominant cellular life in the sea;– generally, there are about 1 million to 10 million viruses in each mL of seawater, or about ten times more double-stranded DNA viruses than there are cellular organisms, although estimates of viral abundance in seawater can vary over a wide range. Tailed bacteriophages appear to dominate marine ecosystems in number and diversity of organisms, and bacteriophages belonging to the families Corticoviridae, Inoviridae and Microviridae are also known to infect diverse marine bacteria.
   From a medical standpoint, an important feature of this genus is the high level of antibiotic resistance. Some enterococci are intrinsically resistant to β-lactam-based antibiotics (penicillins, cephalosporins, carbapenems), as well as many aminoglycosides. In the last two decades, particularly virulent strains of "Enterococcus" that are resistant to vancomycin (vancomycin-resistant "Enterococcus", or VRE) have emerged in nosocomial infections of hospitalized patients, especially in the US. Other developed countries, such as the UK, have been spared this epidemic, and, in 2005, Singapore managed to halt an epidemic of VRE. VRE may be treated with quinupristin/dalfopristin (Synercid) with response rates around 70%.
   The mechanisms for infection, proliferation, and persistence of a virus in cells of the host are crucial for its survival. For example, some diseases such as measles employ a strategy whereby it must spread to a series of hosts. In these forms of viral infection, the illness is often treated by the body's own immune response, and therefore the virus is required to disperse to new hosts before it is destroyed by immunological resistance or host death. In contrast, some infectious agents such as the Feline leukemia virus, are able to withstand immune responses and are capable of achieving long-term residence within an individual host, whilst also retaining the ability to spread into successive hosts.
   Often, the degree of cross-immunity between virus strains is assumed to be related to their sequence distance.
   Bacterial and viral meningitis are contagious, but neither is as contagious as the common cold or flu. Both can be transmitted through droplets of respiratory secretions during close contact such as kissing, sneezing or coughing on someone, but cannot be spread by only breathing the air where a person with meningitis has been. Viral meningitis is typically caused by enteroviruses, and is most commonly spread through fecal contamination. The risk of infection can be decreased by changing the behavior that led to transmission.
  
  Section::::Prevention.:Vaccination.
   During 2008-2012, 4,613 cases of "E. chaffeensis" infections were reported through the National Notifiable Diseases Surveillance System (NNDSS). The incidence rate (IR) was 3.2 cases per million person-years (PYs). The hospitalization rate (HR) was 57% and the case fatality rate (CFR) was 1%. During that same time, 55 cases of "E. ewingii" infections were reported through NNDSS. The national IR was 0.04 cases per million PY. The HR was 77% and the case fatality rate was 0%.
   Section::::Epidemiology.
  
  Lower respiratory infectious disease is the fifth-leading cause of death and the combined leading infectious cause of death, being responsible for 2.74 million deaths worldwide. This is generally similar to estimates in the 2010 Global Burden of Disease study.
  
  This total only accounts for "Streptococcus pneumoniae" and "Haemophilus Influenzae" infections and does not account for atypical or nosocomial causes of lower respiratory disease, therefore underestimating total disease burden.
  
  Section::::Society and culture.
  
  Lower respiratory tract infections place a considerable strain on the health budget and are generally more serious than upper respiratory infections.
   The human virome is a part of our bodies and will not always cause harm. Many latent and asymptomatic viruses are present in the human body all the time. Viruses infect all life forms; therefore the bacterial, plant, and animal cells and material in our gut also carry viruses. When viruses cause harm by infecting the cells in the body, a symptomatic disease may develop. Contrary to common belief, harmful viruses may be in the minority compared to benign viruses in the human body. It is much harder to identify viruses than it is to identify bacteria, therefore our understanding of benign viruses in the human body is very rudimentary.
   Infectious diseases are commonly transmitted from person to person through direct contact. The types of contact are through person to person and droplet spread. Indirect contact such as airborne transmission, contaminated objects, food and drinking water, animal person contact, animal reservoirs, insect bites, and environmental reservoirs are another way infectious diseases are transmitted,
  
  Section::::Classification.:By anatomic location.
  
  Infections can be classified by the anatomic location or organ system infected, including:
  
  BULLET::::- Urinary tract infection
  
  BULLET::::- Skin infection
  
  BULLET::::- Respiratory tract infection
  
  BULLET::::- Odontogenic infection (an infection that originates within a tooth or in the closely surrounding tissues)
  
  BULLET::::- Vaginal infections
   Bloodstream-sourced osteomyelitis is seen most frequently in children, and nearly 90% of cases are caused by "Staphylococcus aureus". In infants, "S. aureus", Group B streptococci (most common) and "Escherichia coli" are commonly isolated; in children from one to 16 years of age, "S. aureus", "Streptococcus pyogenes", and "Haemophilus influenzae" are common. In some subpopulations, including intravenous drug users and splenectomized patients, Gram-negative bacteria, including enteric bacteria, are significant pathogens.
   The leading cause of death worldwide is cardiovascular disease, but infectious diseases are the second leading cause of death worldwide and the leading cause of death in infants and children.
  
  Section::::Other causes.
  
  Other causes or associations of disease are: a compromised immune system, environmental toxins, radiation exposure, diet and lifestyle choices, stress, and genetics. Diseases may also be multifactorial, requiring multiple factors to induce disease. For example: in a murine model, Crohn's disease can be precipitated by a norovirus, but only when both a specific gene variant is present and a certain toxin has damaged the gut.
   The advantage of estimating "S" in this way is that both the average age of infection and average life expectancy will be well documented, and thus the other parameters needed to calculate "S" will be easily at hand.
  
  The parameter "S" is important in the mathematical modelling of epidemics.
  
  Section::::Susceptibility in virology.
  
  Viruses are only able to cause disease or pathologies if they meet several criteria:
  
  BULLET::::1. The virus is able to enter the cell (called a susceptible state)
  
  BULLET::::2. There is a sufficient number of viruses within the cell
  