susceptibility to some infectious diseases, such as pneumonia and tuberculosis [38]. However, some research has suggested that risky behaviours associated with affluent lifestyles can decrease during recessions [27,57], depending on the price and availability of the substances in question [30,45]. The implications for infectious disease are not, however, known. Other factors may also reduce immunity during an economic downturn, but the links are indirect. There is some evidence linking stress to impaired immunological status, by virtue of the cortisol response, increasing susceptibility to certain infectious diseases, [49] [48] although responses to stress vary greatly between individuals [58]. Meanwhile, governments which do not provide food subsidies to indigent populations when faced with rising food prices risk impairing nutrition, a risk factor for several infectious diseases that appears to reflect weakening immunolog- ical defences against latent infections, for example, reactivation of tuberculosis [38]. ii. Recovery Rate (Infected to Recovered) We found evidence for reduced treatment efficacy and availability; delays prior to accessing therapy arising from reduced detection or longer periods to initiate treatment; development of resistance and reduced treatment adherence; and evidence for higher mortality (albeit reducing the infectious period) (Figure 1). Much of the evidence relates, on the supply side, to public provision of healthcare services, and on the demand side, to citizen access to the healthcare system. Most of the papers we identified addressed the former. In periods of economic crisis, countries tend to reduce public spending, either to accommodate a tightened fiscal environment, or to adhere to the terms of loans from international donors. Public spending cuts may affect health adversely. One study, for example, suggested that recipients of International Monetary Fund (IMF) loans experienced reductions in public spending (roughly 7.7%), which led to fewer doctors per capita (7.5%) and slower progress in rolling out the WHO- recommended DOTS programme for TB (45%). Overall, loan recipients experienced increases in TB incidence (13.9%), prevalence (13.3%) and mortality (16.6%). This trend is not only related to nations in receipt of loans. One study reported how closure of health district health centres due to budget cuts during New York City’s fiscal crisis in the 1990s led to a failure in follow-up treatment and screening, as well as inadequate availability of front-line drugs. TB incidence rose and the share of reported cases that were multidrug resistant increased from 10% to 25%. Closure of units responsible for HIV control also coincided with significant rises in reported HIV infections, doubling between 1985 and 1990 from 250,000 to 500,000 [52]. One study in Croatia during the 1993 post-war economic recession found that, after the health service closed anti- tuberculosis dispensaries and allocated responsibility for care for tuberculosis to general practitioners, there was an observed increase in diagnostic delays and diminished compliance to TB treatment [59]. Similarly, significant reductions in public sector healthcare provision, especially among low-income groups, during Mexico’s financial crisis in 1994–1995 corresponded to a rise in infectious disease mortality rates by 6% [60]. During the South Asian economic crisis of the mid-1990s, there were recessions in both Thailand and Malaysia. However, while the Thai government opted for significant cuts in health expenditure, the Malaysian government increased expenditure on primary care. The Thai government’s decision to disinvest in health promotion and HIV/ AIDS control was associated with a rise in incidence of AIDS by 2% as well as rises in incidence of STDs and malaria, and a Economic Crises and Infectious Diseases decline in the numbers of immunised children [61]. No such rises were observed in Malaysia at the time, even though numbers of immunized children also decreased. On the demand side, several factors can lead to reductions in healthcare access by citizenries under financial strain. Public spending on health is vulnerable during an economic downturn; in the USA between 1980 and 1982, reductions in spending were associated with raised incidence of syphilis, tuberculosis, and genitourinary infections as well as diminished immunisation rates among children [62]. Reports further suggest that due to the economic crisis, the poor, especially in countries with high degrees of out-of-pocket spending, are unable to effectively utilize healthcare services and prescribed treatments due to inability to afford co-payments to visit or stay in a health facility or buy prescription drugs [8]. A study of the financial crisis in Peru during the late 1980s reported a 2.5% increase in mortality among children born during this period, attributed to reduced access to health care [63]. Evidence is mixed on the impact of economic downturns on mortality rates. Five studies identified statistically significant associations of rise in unemployment with increases in mortality and morbidity from communicable diseases [27,57,63,64,65], although the causal mechanisms remain unclear. One study found no association between rises in unemployment rates and infectious disease mortality rates in 26 EU countries over the past three decades [29]. Recent reports from the UK indicate a significant rise in winter deaths in 2008, particularly among the elderly [66], attributed to the financial crisis. In contrast, one study of mortality in Germany demonstrated that a 1% increase in unemployment in Germany had the strongest protective effects on pneumonia and influenza in the population older than 65 years [57]; however, no mechanism was proposed for this counter-cyclical effect. iii. Re-introduction rates We found evidence that economic crisis increased the size of high-risk subpopulations and the risk of ‘‘super-spreading environments’’ among such groups, which may include, among others, homeless populations, ethnic minorities, migrants (espe- cially minors), prison inmates, and the poor. Alongside environ- mental factors such as crowded living or working conditions, susceptibility among these groups may be heightened by factors such as lower immunity, deteriorated nutrition, or obstructed access to preventative health care. Several studies found economic hardship increased the population share of high-risk groups. The study of TB incidence during New York City’s crisis in 1975 found that the number of homeless people rose by 60%, a group at very high risk of TB [67]. Overall, risks of contracting TB were greatest among those who had experienced reductions in income, involuntary unemploy- ment, and were unable to afford health care [55,68]. Another high-risk group whose membership tends to increase during economic downturns are migrants, who tend to be at increased risk of infectious diseases and below average access to healthcare services, although there is a great diversity among different migrant groups and their vulnerability is also influenced by their demographics, socio-economic status, social networks, and presence of discrimination as well as disease epidemiology in their country of origin [69]. A different example of large-scale population movements spreading disease occurred in the former Soviet republics, when epidemic spread is thought to have been facilitated by the mass movements of populations [70], especially into prisons [71]. Four studies provided evidence indicating that reduced immunisations among children contributed to infectious disease PLoS ONE | www.plosone.org 9 June 2011 | Volume 6 | Issue 6 | e20724