if the illness is acute or symptoms persist and medications are needed to treat it, a nitroimidazole medication is used such as metronidazole, tinidazole, secnidazole or ornidazole. the world health organization and infectious disease society of america recommend metronidazole as first line therapy. the us cdc lists metronidazole, tinidazole, and nitazoxanide as effective first-line therapies; of these three, only nitazoxanide and tinidazole are approved for the treatment of giardiasis by the us fda. a meta-analysis published by the cochrane collaboration in 2012 found that compared to the standard of metronidazole, albendazole had equivalent efficacy while having fewer side effects, such as gastrointestinal or neurologic issues. other meta-analyses have reached similar conclusions. both medications need a five to 10 day long course; albendazole is taken once a day, while metronidazole needs to be taken three times a day. the evidence for comparing metronidazole to other alternatives such as mebendazole, tinidazole or nitazoxanide was felt to be of very low quality. while tinidazole has side effects and efficacy similar to those of metronidazole, it is administered with a single dose. resistance has been seen clinically to both nitroimidazoles and albendazole, but not nitazoxanide, though nitazoxanide resistance has been induced in research laboratories. the exact mechanism of resistance to all of these medications is not well understood. in the case of nitroimidazole-resistant strains of giardia, other drugs are available which have showed efficacy in treatment including quinacrine, nitazoxanide, bacitracin zinc, furazolidone and paromomycin. mepacrine may also be used for refractory cases. probiotics, when given in combination with the standard treatment, has been shown to assist with clearance of giardia. during pregnancy, paromomycin is the preferred treatment drug because of its poor intestinal absorption, resulting in less exposure to the fetus. alternatively, metronidazole can be used after the first trimester as there has been wide experience in its use for trichomonas in pregnancy. prognosis in people with a properly functioning immune system, infection may resolve without medication. a small portion, however, develop a chronic infection. people with an impaired immune system are at higher risk of chronic infection. medication is an effective cure for nearly all people although there is growing drug-resistance. children with chronic giardiasis are at risk for failure to thrive as well as more long-lasting sequelae such as growth stunting. up to half of infected people develop a temporary lactose intolerance leading symptoms that may mimic a chronic infection. some people experience post-infectious irritable bowel syndrome after the infection has cleared. giardiasis has also been implicated in the development of food allergies. this is thought to be due to its effect on intestinal permeability. epidemiology rates of giardiasis in 2005 in the united states in some developing countries giardia is present in 30% of the population. in the united states it is estimated that it is present in 3–7% of the population. the number of reported cases in the united states in 2018 was 15,584. all states that classify giardiasis as a notifiable disease had cases of giardiasis. the states of illinois, kentucky, mississippi, north carolina, oklahoma, tennessee, texas, and vermont did not notify the center for disease control regarding cases in 2018. the states with the highest number of cases in 2018 were california, new york, florida, and wisconsin. there are seasonal trends associated with giardiasis. july, august, and september are the months with the highest incidence of giardiasis in the united states. in the ecdc's (european centre for disease prevention and control) annual epidemiological report containing 2014 data, 17,278 confirmed giardiasis cases were reported by 23 of the 31 countries that are members of the eu/eea. germany reported the highest number at 4,011 cases. following germany, the uk reported 3,628 confirmed giardiasis cases. together, this accounts for 44% of total reported cases. research some intestinal parasitic infections may play a role in irritable bowel syndrome and other long-term sequelae such as chronic fatigue. the mechanism of transformation from cyst to trophozoites has not been characterized but may be helpful in developing drug targets for treatment-resistant giardia. the interaction between giardia and host immunity, internal flora, and other pathogens is not well understood. the main congress about giardiasis is the "international giardia and cryptosporidium conference" (igcc). a summary of results presented at the most recent edition (2019, in rouen, france) is available. other animals in both dogs and cats, giardiasis usually responds to metronidazole and fenbendazole. metronidazole in pregnant cats can cause developmental malformations. many cats dislike the taste of fenbendazole. giardiasis has been shown to decrease weight in livestock.