More than 300 million people worldwide have asthma. The rate of asthma increases as countries become more urbanized and in many parts of the world those who develop asthma do not have access to medication and medical care. Within the United States, African Americans and Latinos are four times more likely to suffer from severe asthma than whites. The disease is closely tied to poverty and poor living conditions. Asthma is also prevalent in children in low income countries. Homes with roaches and mice, as well as mold and mildew put children at risk for developing asthma as well as exposure to cigarette smoke.

Unlike many other Western countries, the mortality rate for asthma has steadily risen in the United States over the last two decades. Mortality rates for African American children due to asthma are also far higher than that of other racial groups. For African Americans, the rate of visits to the emergency room is 330 percent higher than their white counterparts. The hospitalization rate is 220 percent higher and the death rate is 190 percent higher. Among Hispanics, Puerto Ricans are disporpotionatly affected by asthma with a disease rate that is 113 percent higher than non-Hispanic Whites and 50 percent higher than non-Hispanic Blacks. Studies have shown that asthma morbidity and mortality are concentrated in inner city neighborhoods characterized by poverty and large minority populations and this affects both genders at all ages. Asthma continues to have an adverse effects on the health of the poor and school attendance rates among poor children. 10.5 million days of school are missed each year due to asthma.

Though heart disease is not exclusive to the poor, there are aspects of a life of poverty that contribute to its development. This category includes coronary heart disease, stroke and heart attack. Heart disease is the leading cause of death worldwide and there are disparities of morbidity between the rich and poor. Studies from around the world link heart disease to poverty. Low neighborhood income and education were associated with higher risk factors. Poor diet, lack of exercise and limited (or no) access to a specialist were all factors related to poverty, though to contribute to heart disease.

Both low income and low education were predictors of coronary heart disease, a subset of cardiovascular disease. Of those admitted to hospital in the United States for heart failure, women and African Americans were more likely to reside in lower income neighborhoods. In the developing world, there is a 10 fold increase in cardiac events in the black and urban populations.

A study conducted on 452 patients revealed that the genotype responsible for higher IL-10 expression makes HIV infected people more susceptible to tuberculosis infection. Another study on HIV-TB co-infected patients also concluded that higher level of IL-10 and IL-22 makes TB patient more susceptible to Immune reconstitution inflammatory syndrome (IRIS). It is also seen that HIV co-infection with tuberculosis also reduces concentration of immunopathogenic matrix metalloproteinase (MMPs) leading to reduced inflammatory immunopathology.

The immune reconstitution inflammatory syndrome (IRIS) has been described in those with normal immune function with meningitis caused by "C. gattii" and "C. grubii". Several weeks or even months into appropriate treatment, there can be deterioration with worsening meningitis symptoms and progression or development of new neurological symptoms. IRIS is however much more common in those with poor immune function (≈25% vs. ≈8%).

Magnetic resonance imaging shows increase in the size of brain lesions, and CSF abnormalities (white cell count, protein, glucose) increase. Radiographic appearance of cryptococcal IRIS brain lesions can mimic that of toxoplasmosis with ring enhancing lesions on head computed tomography (CT). CSF culture is sterile, and there is no increase in CSF cryptococcal antigen titre.

The increasing inflammation can cause brain injury or be fatal.

The mechanism behind IRIS in cryptococcal meningitis is primarily immunologic. With reversal of immunosuppression, there is paradoxical increased inflammation as the recovering immune system recognises the fungus. In severe IRIS cases, treatment with systemic corticosteroids has been utilized - although evidence-based data are lacking.

Cryptococcosis is a defining opportunistic infection for AIDS, and is the second-most-common AIDS-defining illness in Africa. Other conditions that pose an increased risk include certain lymphomas (e.g., Hodgkin's lymphoma), sarcoidosis, liver cirrhosis, and patients on long-term corticosteroid therapy.

Distribution is worldwide in soil. The prevalence of cryptococcosis has been increasing over the past 20 years for many reasons, including the increase in incidence of AIDS and the expanded use of immunosuppressive drugs.

In humans, "C. neoformans" causes three types of infections:

- Wound or cutaneous cryptococcosis

- Pulmonary cryptococcosis

- Cryptococcal meningitis.

Cryptococcal meningitis (infection of the meninges, the tissue covering the brain) is believed to result from dissemination of the fungus from either an observed or unappreciated pulmonary infection. Often there is also silent dissemination throughout the brain when meningitis is present. "Cryptococcus gattii" causes infections in immunocompetent people (fully functioning immune system), but "C. neoformans v. grubii", and "v. neoformans" usually only cause clinically evident infections in persons with some form of defect in their immune systems (immunocompromised persons). People with defects in their cell-mediated immunity, for example, people with AIDS, are especially susceptible to disseminated cryptococcosis. Cryptococcosis is often fatal, even if treated. It is estimated that the three-month case-fatality rate is 9% in high-income regions, 55% in low/middle-income regions, and 70% in sub-Saharan Africa. As of 2009 there were globally approximately 958,000 annual cases and 625,000 deaths within three months after infection.

Although the most common presentation of cryptococcosis is of "C. neoformans" infection in an immunocompromised person (such as persons living with AIDS), the "C. gattii" is being increasingly recognised as a pathogen in what is presumed to be immunocompetent hosts, especially in Canada and Australia. This may be due to rare exposure and high pathogenicity, or to unrecognised isolated defects in immunity, specific for this organism.

In most cases, the prognosis of mucormycosis is poor and has varied mortality rates depending on its form and severity. In the rhinocerebral form, the mortality rate is between 30% and 70%, whereas disseminated mucormycosis presents with the highest mortality rate in an otherwise healthy patient, with a mortality rate of up to 90%. Patients with AIDS have a mortality rate of almost 100%. Possible complications of mucormycosis include the partial loss of neurological function, blindness and clotting of brain or lung vessels.

With the decrease in the death rate among people with HIV/AIDS receiving new treatments in the 1990s, the rates and severity of epidemic KS also decreased. However, the number of people living with HIV/AIDS is increasing in the United States, and it is possible that the number of people with AIDS-associated Kaposi sarcoma will again rise as these people live longer with HIV infection.

When HIV-negative children take isoniazid after they have been exposed to tuberculosis, their risk to contract tuberculosis is reduced. A Cochrane review investigated whether giving isoniazid to HIV-positive children can help to prevent this vulnerable group from getting tuberculosis. They included three trials conducted in South Africa and Botswana and found that isoniazid given to all children diagnosed with HIV may reduce the risk of active tuberculosis and death in children who are not on antiretroviral treatment. For children taking antiretroviral medication, no clear benefit was detected.

Mucormycosis is a very rare infection, and as such, it is hard to note histories of patients and incidence of the infection. However, one American oncology center revealed that mucormycosis was found in 0.7% of autopsies and roughly 20 patients per every 100,000 admissions to that center. In the United States, mucormycosis was most commonly found in rhinocerebral form, almost always with hyperglycemia and metabolic acidosis (e.g. DKA). In most cases the patient is immunocompromised, although rare cases have occurred in which the subject was not; these are usually due to a traumatic inoculation of fungal spores. Internationally, mucormycosis was found in 1% of patients with acute leukemia in an Italian review.

Infection is through contaminated material such as earth, water, uncooked or cross-contaminated food that has been in contact with the feces of an infected individual or animal. Contact must then be transferred to the mouth and swallowed. It is especially prevalent amongst those in regular contact with bodies of fresh water including recreational water such as swimming pools. Other potential sources include insufficiently treated water supplies, contaminated food, or exposure to feces. The high resistance of "Cryptosporidium" oocysts to disinfectants such as chlorine bleach enables them to survive for long periods and still remain infective. Some outbreaks have happened in day care related to diaper changes.

The following groups have an elevated risk of being exposed to "Cryptosporidium":

- Child care workers

- Parents of infected children

- People who take care of other people with cryptosporidiosis

- International travelers

- Backpackers, hikers, and campers who drink unfiltered, untreated water

- People, including swimmers, who swallow water from contaminated sources

- People who handle infected cattle

- People exposed to human feces through sexual contact

Cases of cryptosporidiosis can occur in a city that does not have a contaminated water supply. In a city with clean water, it may be that cases of cryptosporidiosis have different origins. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. "Cryptosporidium" is causing serious illness more frequently in immunocompromised than in apparently healthy individuals. It may chronically sicken some children, as well as adults who are exposed and immunocompromised. A subset of the immunocompromised population is people with AIDS. Some sexual behaviors can transmit the parasite directly.

Cryptosporidiosis is found worldwide. It causes 50.8% of water-borne diseases that are attributed to parasites. In developing countries, 8–19% of diarrheal diseases can be attributed to "Cryptosporidium". Ten percent of the population in developing countries excretes oocysts. In developed countries, the number is lower at 1–3%. The age group most affected are children from 1 to 9 years old.

Roughly 30% of adults in the United States are seropositive for cryptosporidiosis, meaning that they contracted the infection at some point in their lives.

Avoiding food or water that may be contaminated with stool can help prevent the infection of "Cystoisospora" (Isosporiasis). Good hand-washing, and personal-hygiene practices should be used as well. One should wash their hands with soap and warm water after using the toilet, changing diapers, and before handling food (CDC.gov). It is also important to teach children the importance of washing their hands, and how to properly wash their hands.

The cause of immunodeficiency varies depending on the nature of the disorder. The cause can be either genetic or acquired by malnutrition and poor sanitary conditions. Only for some genetic causes, the exact genes are known. Although there is no true discrimination to who this disease affects, the genes are passed from mother to child, and on occasion from father to child. Women tend not to show symptoms due to their second X chromosome not having the mutation while man are symptomatic, due to having one X chromosome.

HIV is transmitted by three main routes: sexual contact, significant exposure to infected body fluids or tissues, and from mother to child during pregnancy, delivery, or breastfeeding (known as vertical transmission). There is no risk of acquiring HIV if exposed to feces, nasal secretions, saliva, sputum, sweat, tears, urine, or vomit unless these are contaminated with blood. It is possible to be co-infected by more than one strain of HIV—a condition known as HIV superinfection.

Pneumocystosis is an infection by "Pneumocystis jirovecii"that primarily occurs as a pulmonary infection AIDS patients, with extrapulmonary involvement being uncommon but, if occurring in the skin, presenting most often as nodular growths in the auditory canal.

HIV/AIDS has become a chronic rather than an acutely fatal disease in many areas of the world. Prognosis varies between people, and both the CD4 count and viral load are useful for predicted outcomes. Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype. After the diagnosis of AIDS, if treatment is not available, survival ranges between 6 and 19 months. HAART and appropriate prevention of opportunistic infections reduces the death rate by 80%, and raises the life expectancy for a newly diagnosed young adult to 20–50 years. This is between two thirds and nearly that of the general population. If treatment is started late in the infection, prognosis is not as good: for example, if treatment is begun following the diagnosis of AIDS, life expectancy is ~10–40 years. Half of infants born with HIV die before two years of age without treatment.

The primary causes of death from HIV/AIDS are opportunistic infections and cancer, both of which are frequently the result of the progressive failure of the immune system. Risk of cancer appears to increase once the CD4 count is below 500/μL. The rate of clinical disease progression varies widely between individuals and has been shown to be affected by a number of factors such as a person's susceptibility and immune function; their access to health care, the presence of co-infections; and the particular strain (or strains) of the virus involved.

Tuberculosis co-infection is one of the leading causes of sickness and death in those with HIV/AIDS being present in a third of all HIV-infected people and causing 25% of HIV-related deaths. HIV is also one of the most important risk factors for tuberculosis. Hepatitis C is another very common co-infection where each disease increases the progression of the other. The two most common cancers associated with HIV/AIDS are Kaposi's sarcoma and AIDS-related non-Hodgkin's lymphoma. Other cancers that are more frequent include anal cancer, Burkitt's lymphoma, primary central nervous system lymphoma, and cervical cancer.

Even with anti-retroviral treatment, over the long term HIV-infected people may experience neurocognitive disorders, osteoporosis, neuropathy, cancers, nephropathy, and cardiovascular disease. Some conditions like lipodystrophy may be caused both by HIV and its treatment.

The coccidian parasite "Isospora belli" infects the epithelial cells of the small intestine, and is the least common of the three intestinal coccidia that infect humans ("Toxoplasma", "Cryptosporidium", and "Isospora").

The disease PCP is relatively rare in people with normal immune systems, but common among people with weakened immune systems, such as premature or severely malnourished children, the elderly, and especially persons living with HIV/AIDS (in whom it is most commonly observed). PCP can also develop in patients who are taking immunosuppressive medications. It can occur in patients who have undergone solid organ transplantation or bone marrow transplantation and after surgery. Infections with "Pneumocystis" pneumonia are also common in infants with hyper IgM syndrome, an X-linked or autosomal recessive trait.

The causative organism of PCP is distributed worldwide and "Pneumocystis" pneumonia has been described in all continents except Antarctica. Greater than 75% of children are seropositive by the age of 4, which suggests a high background exposure to the organism. A post-mortem study conducted in Chile of 96 persons who died of unrelated causes (suicide, traffic accidents, and so forth) found that 65 (68%) of them had pneumocystis in their lungs, which suggests that asymptomatic pneumocystis infection is extremely common.

"Pneumocystis jirovecii" was originally described as a rare cause of pneumonia in neonates. It is commonly believed to be a commensal organism (dependent upon its human host for survival). The possibility of person-to-person transmission has recently gained credence, with supporting evidence coming from many different genotyping studies of "Pneumocystis jirovecii" isolates from human lung tissue. For example, in one outbreak of 12 cases among transplant patients in Leiden, it was suggested as likely, but not proven, that human-to-human spread may have occurred.

Prognosis depends greatly on the nature and severity of the condition. Some deficiencies cause early mortality (before age one), others with or even without treatment are lifelong conditions that cause little mortality or morbidity. Newer stem cell transplant technologies may lead to gene based treatments of

debilitating and fatal genetic immune deficiencies. Prognosis of acquired immune deficiencies depends on avoiding or treating the causative agent or

condition (like AIDS).

"Pneumocystis" pneumonia (PCP) is a form of pneumonia, caused by the yeast-like fungus "Pneumocystis jirovecii".

"Pneumocystis" pneumonia is not commonly found in the lungs of healthy people, but, being a source of opportunistic infection, it can cause a lung infection in people with a weak immune system. "Pneumocystis" pneumonia is especially seen in people with cancer undergoing chemotherapy, HIV/AIDS, and the use of medications that suppress the immune system.

Primary cerebral lymphoma (or "primary central nervous system lymphoma") is a form of NHL. It is very rare in immunocompetent people, with an incidence of 5–30 cases per million person-years. However the incidence in immunocompromised individuals is greatly increased, up to 100 per million person-years.

Primary cerebral lymphoma is strongly associated with Epstein–Barr virus (EBV). The presence of EBV DNA in cerebrospinal fluid is highly suggestive of primary cerebral lymphoma.

Treatment of AIDS patients with antiretroviral drugs reduces the incidence of primary cerebral lymphoma.

Among individuals being treated in intensive care units, the mortality rate is about 30-50% when systemic candidiasis develops.

Bats recovering from white-nose syndrome (WNS) may be the first natural occurrence of IRIS, in a report released by the USGS. WNS is typified by a cutaneous infection of the fungus "Pseudogymnoascus destructans" during hibernation, when the immune system is naturally suppressed to conserve energy through the winter. This study suggests that bats undergoing an intense inflammation at the site of infection after a return to euthermia is a form of IRIS.

Blood tests to detect antibodies against KSHV have been developed and can be used to determine whether a person is at risk for transmitting infection to their sexual partner, or whether an organ is infected prior to transplantation. However, these tests are not available except as research tools, and, thus, there is little screening for persons at risk for becoming infected with KSHV, such as people following a transplant.

Much of the deadliness of the epidemic in Sub-Saharan Africa is caused by a deadly synergy between HIV and tuberculosis, termed a "co-epidemic". The two diseases have been "inextricably bound together" since the beginning of the HIV epidemic. "Tuberculosis and HIV co-infections are associated with special diagnostic and therapeutic challenges and constitute an immense burden on healthcare systems of heavily infected countries like Ethiopia." In many countries without adequate resources, the tuberculosis case rate has increased five to ten-fold since the identification of HIV. Without proper treatment, an estimated 90 percent of persons living with HIV die within months after contracting tuberculosis. The initiation of highly active antiretroviral therapy in persons coinfected with tuberculosis can cause an immune reconstitution inflammatory syndrome with a worsening, in some cases severe worsening, of tuberculosis infection and symptoms.

An estimated 874,000 people in Sub-Saharan Africa were living with both HIV and tuberculosis in 2011, with 330,000 in South Africa, 83,000 in Mozambique, 50,000 in Nigeria, 47,000 in Kenya, and 46,000 in Zimbabwe. In terms of cases per 100,000 population, Swaziland's rate of 1,010 was by far the highest in 2011. In the following 20 African countries, the cases-per-100,000 coinfection rate has increased at least 20 percent between 2000 and 2011: Algeria, Angola, Chad, Comoros, Republic of the Congo, Democratic Republic of the Congo, Equatorial Guinea, The Gambia, Lesotho, Liberia, Mauritania, Mauritius, Morocco, Mozambique, Senegal, Sierra Leone, South Africa, Swaziland, Togo, and Tunisia.

Since 2004, however, tuberculosis-related deaths among people living with HIV have fallen by 28 percent in Sub-Saharan Africa, which is home to nearly 80 percent of the people worldwide who are living with both diseases.